Piero Scaruffi

Inside the Brain Life is not the only field in which traditional Physics seems to be powerful to offer comprehensive explanations. The brain is another system that seems to obey laws that only partially reflect the linear universe implied by Physics. Explaining the evolution of life required a new paradigm, the paradigm of "design without a designer". It turns out that the functioning of the brain (that is responsible for the evolution of our thoughts) requires a similar paradigm. Connectionism Human memory may be deficient in many ways (it forgets, it does not remember "photographically"), but somehow it is extremely good at recognizing. I recognize a friend even if he grew a beard, even if he's wearing different clothes every day, even if I see him sideways, and from any possible angle. How can I recognize all those images as the same image if they are all different? It is almost impossible to take the identical shot of a person twice: some details will always be different: how can I recognize that it is the same person, if the image is always different? I can show you two pictures of a street, taken at different times: you will recognize them as pictures of the same street. But there are probably countless differences: cars that were parked moved away and new cars took their places, pedestrians that were walking are gone, dogs and birds have changed positions, smoke has blown away, all the leaves of all the trees have moved because of the breeze, etc. How do you recognize that it is the same street, if the image of that street is never the same? Even a baby recognizes that an object turned sideways is still the same object, even if it looks completely different. Take a box and rotate it 45 degrees: it now looks like a completely different geometric figure. Nonetheless, a baby can recognize that it is the same object. The key to understanding our memory may lie in the peculiar structure of our brain. Unlike most of our artifacts, which are designed to be modular, hierarchical and linear, a brain is an amazingly intricate piece of work. The brain does not work the way our artifacts work. There seems to be no "designer" that specifies what has to be designed. There seems to be a huge number of connected units, none of which prevails and all of which cooperate in some fashion to produce what transpires as "intelligent" behavior. At the end of the 19th century, the USA psychologist William James had a number of powerful intuitions: 1. that the brain is built to ensure survival in the world; 2. that cognitive faculties cannot be abstracted from the environment that they deal with; 3. that the brain is organized as an associative network; 4. that associations are governed by a rule of reinforcement. The latter two (3 and 4) laid the foundations for the "connectionist" model of the brain. The former two (1 and 2) laid the foundations for a cognitive model grounded in a Darwinian scenario of survival of the fittest. Selective Behavior Other psychologists contributed, directly or indirectly, to the connectionist model of the brain. In the 1920s behaviorist scientists such as the Russian physiologist Ivan Pavlov and the USA psychologist Burrhus Skinner were influential in emphasizing the simple but pervasive law of learning through "conditioning": if an unconditioned stimulus (e.g., a bowl of meat) that normally causes an unconditioned response (e.g., the dog salivates) is repeatedly associated with a conditioned stimulus (e.g., a bell), the conditioned stimulus (the bell) will eventually cause the unconditioned response (the dog salivates) without any need for the unconditioned stimulus (the bowl of meat). Behaviorists came to believe that all forms of learning could be reduced to conditioning phenomena. To Skinner, all learned behavior is the result of selective "reinforcement" of random responses. Mental states (what goes on in our minds) have no effect on our actions. Skinner did not deny the existence of mental states, he simply denied that they explain behavior. A person does what she does because she has been "conditioned" to do that, not because her mind decided so. Skinner noticed a similarity between reinforcement and natural selection: random mutations are "selected" by the environment, and random behavior is also selected by the environment. A random action can bring reward (from the environment) that will cause reinforcement and therefore will increase the chances that the action is repeated in the future. An action that does not bring reward will not be repeated. The environment determines which behavior is learned, just like the environment determines which species evolve. Cognition Gestalt psychologists, instead, focused on higher cognitive processes and opposed the idea that the individual stimulus could cause an individual response. For example, in 1938 the German psychologist Max Wertheimer claimed that perception ought to be more than the sum of the perceived things, i.e. that the whole is more than the sum of the parts. He showed, for example, how one can alter the parts of a melody but the listener would still recognize the melody. Perception of the whole does not depend on perception of all of its parts. We recognize the shape of a landscape way before we recognize each tree and rock in the landscape, and we recognize that a tree is a tree before we recognize what kind of tree it is, because recognizing the species requires an analysis of its parts. Already in the 1920s the German psychologist Wolfgang Koehler had claimed that most problem-solving is not due to a decomposition of the problem but to sudden insight. One may not recognize a familiar face for a few seconds, and then suddenly recognize it. This is not due to a myriad calculations, but to a sudden insight that cannot be broken down into atomic processes. It is just a sudden insight. The German neurologist Kurt Goldstein viewed the organism as a system that has to struggle in order to cope with the challenges of the environment and of its own body. The organism cannot be divided into "organs" and far less into "mind" and "body", because it is the whole that reacts to the environment. Nothing is independent within the organism. The organism is a whole. "Disease" is a manifestation of a change of state between the organism and its environment. Healing does not come through "repair" but through adaptation. The organism cannot simply return to the state preceding the event that changed it, but has to adapt to the conditions that caused the new state. In particular, a local symptom is not meaningful to understand a "disease", and the organism's behavior during a disease is hardly explained as a response to that specific symptom. A patient's body will often undergo mass-scale adjustments. Goldstein emphasizes the ability of organisms to adjust to catastrophic breakdowns of their most vital (mental or physical) functions. The organism's reaction is often a redistribution of its (mental or physical) faculties. Coherently, gestalt psychologists claimed that form is the elementary unit of perception. We do not construct a perception by analyzing a myriad data. We perceive the form as a whole. Around 1950 experiments by the USA neurologist Karl Lashley confirmed that intuition: a lesion in the brain does not necessarily cause a change in the response. Lashley concluded that functions are not localized but distributed around the brain, that there are no specialized areas, that all cortical areas are equally "potent" in carrying out mental functions (this was his "principle of equipotentiality"). Lashley realized that this architecture yields a tremendous advantage: the brain as a whole is "fault tolerant", because no single part is essential to the functioning of the whole. Lashley also enunciated a second principle that can be viewed as its dual, the principle of "mass action": every brain region partakes (to some extent) in all brain processes. Lashley even imagined that memory behaved like an electromagnetic field and that a specific memory was a wave within that field. While he never came to appreciate the importance of the "connections", Lashley's ideas were sort of complementary to the ideas of connectionism. Functions are indeed localized in the brain, but the processing of information inside the brain involves "mass action". The function of analyzing data from the retina is localized in a specific region of the brain, but the function of "seeing" is not localized, because it requires processes that are spread around the brain. There are maps of the retina in the brain (even more than one), and there are maps of the entire body in the brain, and they are orderly maps. The brain keeps a map of what is going on in every part of the body. The Primacy Of Connections The USA psychologist Edward Thorndike, a student of William James had already explained how Skinner's reinforcement occurs. Thorndike had been the first psychologist to propose that animals learn based on the outcome of their actions (the "law of effect") and Skinner simply generalized his ideas. Thorndike modeled the mind as a network of connections among its components. Learning occurs when elements are connected. A habit is nothing more than a chain of "stimulus-response" pairs. Behavior is due to the association of stimuli with responses that is generated through those connections. The "law of effect" states that the probability that a stimulus will cause a given response is proportional to the satisfaction that the response has produced in the past. This principle was consistent with both natural selection and behaviorist conditioning/reinforcement. It was also consistent with gestalt holism because in a vast network of connections the relative importance of an individual connection is negligible. Connectionism can be viewed at various levels of the organization of the mind. At the lowest level, it deals with the neural structure of the brain. The brain is reduced to a network of interacting neurons. Each neuron is a fairly simple structure, whose main function is simply to transmit impulses to other neurons. When anything happens to a neuron, it is likely to affect thousands of other neurons because its effects can propagate very quickly from one neuron to the other. From the outside, the only thing that matters is the response of the brain to a certain stimulus. But that response is the result of thousands of messages transmitted from neuron to neuron according to the available connections. A given response to a given stimulus occurs because the connections propagate that stimulus from the first layer of neurons to the rest of the connected neurons until eventually the response is generated by the last layers of neurons. As long as the connections are stable, a given stimulus will always generate the same response. When a connection changes, a different response may be produced. Connections change, in particular, when the brain "learns" something new. The brain "learns" what response is more appropriate to a given stimulus by adjusting the connections so that next time the stimulus will produce the desired response. The functioning of the brain can be summarized as a continuous refining of the connections between neurons. Each connection can be strengthened or weakened by the messages that travel through it. In 1949 the Canadian physiologist Donald Hebb realized that strengthening and weakening of connections depend on how often they are used. If a connection is never used, it is likely to decay, just like any muscle that is not exercised. If it is used very often, it is likely to get reinforced. A Darwinian concept came to play a key role in the organization of the brain: competitive behavior. Connections "compete" to survive. At a higher level, a connectionist organization can be found in the way our mind organizes concepts. Concepts are not independent of each other: a concept is very much defined by the other concepts it relates to. The best definition of a concept is probably in terms of other concepts and the way it relates to them. Concepts also rely on an associative network. Therefore, William James’ four maxims also apply to concepts. Ultimately, the connectionist model explained the functioning of the brain by employing the same paradigm that Darwin had used to explain the evolution of life: design without a designer. The Neural Structure of the Brain The human brain is probably the single most complex structure that we have found in the universe. Even the human genome is simpler. First of all, the brain is really just the upper extremity of the spinal cord. Nerves departing from the spinal cord communicate with the rest of the body. The spinal cord contains the same gray matter of the brain. Most of the human brain is made of two hemispheres, linked by the "corpus callosum", and covered by the cortex. Under the corpus callosum is located one of the main areas of control of behavior, containing the "thalamus", the "hypothalamus" and the "amygdala". The thalamus is a mini-mirror of the cortex: it seems to replicate the same information, but on a smaller scale. The two amygdalae are widely believed to be in charge of emotions: affection, fear and attention originate or are amplified here. The function of the two thalami seems to be to convey signals from the senses to the cortex and from the cortex to the muscles. The amygdala has the power to take over this strategic highway. The hypothalamus, located below the thalamus, is involved in many "autonomic" functions (heartbeat and breathing, but also hunger, lust, fear). It seems, in particular, to be responsible for controlling body temperature (pretty much like a thermostat). When warned by the immune system (via chemicals in the blood stream), that the body is being attacked, the hypothalamus triggers a simultaneous increase in body metabolism and a reduction in blood flow, i.e. a "fever". Behind the hemispheres is the "cerebellum", one of the main areas of integration of stimuli and coordination of action. The cerebellum contains areas like the "pons" that communicate with the rest of the body. The cerebellum is a bit like a miniature brain: it is divided into hemispheres and has a cortex that surrounds these hemispheres. The cerebellum seems to be indispensable for coordinating complex actions such as playing a musical instrument. The cortex is one of the main areas of sensory-motor control. The cortex is by far the largest structure in the brain: in humans, it accounts for about two thirds of the total brain mass. The terms "cortex" and "neocortex" are often used interchangeably because the neocortex constitutes most of the cerebral cortex in humans, but this is not true for other animals. Located at the base of each hemisphere are the hippocampi. The hippocampus is one of the main areas for recalling long-term memory. It takes about three years to consolidate short-term memory into long term memory. For three years the hippocampus is directly responsible for retrieving a memory. After that period, the memory slides into long term memory. Lesions to the hippocampus result in forgetting everything that happened over the last three years and not being able to remember anything ever again for longer than a few seconds. Alternatively, one can view a brain hemisphere as two concentric spheres: the inner one is the limbic system, comprising amygdala, thalamus, hypothalamus and hippocampus; the outer one is the neocortex. The neocortex processes sensory information and channels it to the hippocampus, which then communicates with the other organs of the limbic system. The limbic system appears to be a central processing unit that mediates between sensory input and motor output, between bodily sensations and body movements. In other words, the limbic system appears to be the main connection between mind and body. The limbic system is (evolutionarily speaking) the oldest part of the brain, the part that humans share with all mammals and that is well developed also in other vertebrates. The brain can also be described as made of four lobes: the frontal lobe, that contains the primary motor area; the temporal lobe, that includes the hippocampus and is related to memory; the occipital lobe, concerned with vision; and the parietal lobe, important for spatial relationships and bodily sensations. Finally, the brainstem is the general term for the area of the brain between the thalamus and spinal cord. This is at the bottom of the brain, next to the cerebellum, and represents the brain's connection with the "autonomic" nervous system, the part of the nervous system that regulates functions such as heartbeat, breathing, etc. These are mechanic functions, but even more vital than the higher ones. Dominance Since the "split-brain" studies carried out in the 1960s by the USA psychologist Roger Sperry, it has been held that the two hemispheres control different aspects of mental life: the left hemisphere is dominant for language and speech, the right brain excels at visual and motor tasks and may also be the prevalent source of emotions. This is due to the fact that the two hemispheres are not identical. For example, the speech area of the cortex is much larger in the left hemisphere. The roles of two hemispheres are not so rigid, though: a child whose left hemisphere is damaged will still learn to speak and will simply use the right hemisphere for language functions. Just like it dominates in language, the left hemisphere also dominates in movement. Both hemispheres organize movement of limbs (each hemisphere takes care of the limbs at the opposite side of the body), but the left hemisphere is the one that directs the movement and that stores the feedback (the one that learns skills/ habits). If the two hemispheres are separated, the right limbs keep working normally, but the left limbs become clumsy and are often unable to carry out even simple learned skills like grabbing a glass. Brain asymmetry is not uncommon in other species, but handedness (that individuals always prefer one hand over the other) is uniquely human, and handedness appears to depend on the asymmetry of the hemispheres. The main "bridge" between the two hemispheres is the corpus callosum, but a number of other "commissures" (communication channels) exist, and their purpose is not known. The USA psychologist Ross Buck proposed a decomposition of human behavior that mirrors the "behavior" of each hemisphere. In his view, our behavior is the product of several systems of organization which belong to two big families. The first one is the family of innate special-purpose processing systems (reflexes, instincts, etc.). In general their function is "bodily adaptation" to the environment. In general, their approach is not analytic but holistic and syncretic: they don't "reduce" the situation to its details, they treat it as a whole. In Buck's view, these processes are innate, we don't need to learn them. The second family contains acquired general-purpose processing systems. In general their function is to make sense of the environment. Their approach is sequential and analytic. The former family is associated with the right hemisphere of the brain and is responsible for emotional expression; the latter is associated with the left hemisphere and is responsible for symbolic thinking. The two families cooperate in determining the body's behavior. Asymmetry The central nervous system of all organisms is remarkably symmetrical. That symmetry ends somewhere inside the mammalian brain, as lesions to the same location in different brain hemispheres have proven, particularly the neurological disorder of aphasia. (The loss of language skills, always related to damage to the left hemisphere, a correlation first recognized by the German neurologist Karl Wernicke in 1874, and the loss of spatial skills, related to damage to the right hemisphere, a correlation first recognized by the British neurologist Hughlings Jackson in 1876). The asymmetric function of the mammalian brain is a puzzle because no physical difference has been observed between the two hemispheres. Split-brain research conducted by Roger Sperry and Michael Gazzaniga showed that both hemispheres are capable of performing the same processing. The USA neurologist Lynn Robertson argues that it is a difference in strength rather than in kind. There is a tiny difference in the way the two hemispheres process early perceptual information, the very first data coming from the senses, and that difference gets amplified as it is processed in the two hemispheres. Robertson's theory is that we understand the world at different levels. The world is made of objects that are made of objects. We perceive, recognize and understand objects at all levels of the hierarchy, and we do so in parallel: we do not build a scene from its parts, and we do not split a scene into its parts. Our perception of the world is a cooperative process of both aspects. We recognize both a scene and its parts, because recognition proceeds simultaneously at different scales. Perception is performed by "frequency-sensitive detectors" in the brain. The right hemisphere is better at analyzing low-frequency information, such as spatial information (objects), whereas the left hemisphere is better at processing high-frequency information, such as language. This asymmetry generates a distributed representation of the world that may have been advantageous for evolutionary purposes. This holds for both vision and audition. The right hemisphere is better equipped for high spatial-frequency patterns as well as high sound-frequency patterns. And viceversa. The reason there are no visible differences between the two hemispheres is that they perform the same processing on the same patterns of information. The difference is subtle: each hemisphere has a bias for a range of frequencies. Suspended Animation Besides handedness, there is another feature that sets the human brain apart from other animals. Human brains are rather unusual in that they require a steady supply of oxygen. A few seconds without oxygen are enough to cause permanent damage to the human brain, if not death itself. On the contrary, most animals can live quite a long time in different kinds of suspended animation. Many mammals can hibernate. Most seeds can survive months or even years before germinating. All these living beings are capable of suspending or slowing down their cellular activity until the environmental conditions become favorable to growth. Humans are much more vulnerable to changing environmental conditions. The Life Of Neurons In 1891 the Spanish anatomist Santiago Ramon y Cajal discovered the neuron, the nerve cell which is the elementary unit of processing in the brain. He also discovered that neurons are held together in networks. A brain is made of neurons (nerve cells) which communicate via junctions called synapses. Neurons are the largest cells in the human body. Neurons are extremely simply units that can be viewed as switches. What creates the complexity of the brain is the synapses that connect the neurons. A human brain has about 100 billion neurons (50% in the cortex), with an average of 10,000 synapses per neuron, which yields about 500 trillion synapses. Neurons die and are born all the time. Synapses are destroyed, created and modified even more rapidly. The Italian biologist Luigi Galvani originally suggested that nerve cells were conductors of electricity in the 18th century, but it wasn't until the 1950s that the electrical activity of the brain was explained. The fundamental discovery of the British neurologist John Eccles and others was that neurons communicate via chemicals, generally referred to as "neurotransmitters". Under appropriate conditions, a neuron emits an action potential, which a synapsis converts into a neurotransmitter and sends to other neurons. More precisely, neurotransmitters are synthesized by the cell's body and stored in the synapses until a nerve pulse is generated. This chemical messenger can either excite (start firing an action potential of its own) or inhibit (stop firing the action potential) each receiving neuron. Neurons are binary machines: either they fire, or they don't. If they fire, they release always the same amount of neurotransmitter. Each neuron can synthesize and therefore release only one kind of neurotransmitter. There are about 50 kinds. Each neurotransmitter has a particular effect on receiving neurons and can therefore yield a different "pathway" within the brain. Neurotransmitters do matter. Each seems to have a different kind of message. For example, endorphins is related to pain. Each neuron only releases one kind of chemical (which can contain more than one neurotransmitter, but it is always the same combination). A neurotransmitter can be received only by appropriate receptors. De facto, each neurotransmitter creates a sub-net of neurons. Each seems to contribute to different aspects of mental life. The "intelligence" of the brain is due to the high number of connections, which cause a simple signal to generate a very complex chain reaction of activation of neurons around the brain. This intelligence would be pointless if it didn't relate to the rest of the body. The nervous system extends throughout the body via nerve fibers. There are two kinds of nerve fibers and they are both one-way only: "afferent" nerves connect the senses to the brain, and "efferent" nerves connect the brain to the muscles. The Biorhythms The nervous system is made of two main subdivisions: the central nervous system (the brain and the spinal cord) and the peripheral nervous system (in particular the autonomic nervous system that controls the heartbeat, breathing and other bodily functions). This complex apparatus relies on a number of internal clocks: heartbeat (approximately one per second), breathing (approximately once every 4 seconds), REM sleep (4 or 5 times per night, at approximately 90 minute intervals), sleep/wake or "circadian" (every 24 hours), menstruation (every 28 days), hibernation (every 365 days), the thalamus’ rhythm (40 times a second), the amygdala's rhythm, etc. All these "biorhythms" are registered in the brain, although they cannot be consciously perceived. The synchronization of such a complex system of biorhythms is accomplished by the brain. The suprachiasmatic nucleus (at the base of the hypothalamus), a cluster of about 10,000 neurons, keeps the central clock of the brain, the "circadian" clock, that dictates the day-night cycle of activity. The cells of the suprachiasmatic nucleus perform chemical reactions that take about 24 hours to complete. Those cells are connected to other regions of the brain and the products of their chemical reactions directly affect the activity of those regions. Triggered by the suprachiasmatic nucleus, melatonin secretion starts after sunset, induces sleep and lowers the temperature of the body. Blood pressure starts to rise with sunrise. Then melatonin secretion stops and we wake up. We become more and more alert, as both blood pressure and body temperature increase. At sunset the cycle resumes. Circadian rhythms are so common among species (even plants) that they may be one of the oldest attributes of life. The importance of these clocks cannot be overlooked. The behavior of living organisms changes as the day progresses, because their clocks tell them so. It is not consciousness that tells us what to do: it is our inner clock that dictates much of our behavior. The brain is slave to its clock. A circadian clock is actually present in every cell of the body: an isolated cell in the laboratory still follows a 24-hour cycle. What the suprachiasmatic nucleus does is to synchronize the 24-hour cycles of all the cells in the body. We are controlled by several different clocks rather than by just one clock, a fact that appears to be a senseless complication. Part of the complexity of the brain may be due precisely to the need to "transduce" each of these rhythms into the other ones, otherwise different organs could not cooperate. The operations performed by the various organs of the body occur in continuous quantities, not discrete quantities. For example, we can drink any amount of water (not only some set amounts) and exhale any amount of air. However, the "functioning" of those organs is discrete, not continuous: a clock sets their rhythm. Somehow the body needs to "pace" each of its many internal functions. The clocks may exist precisely because they enable synchronization among wildly different organs that happen to depend on each other. A number of biological clocks (many more than we have discovered so far) may be presiding over all the vital activities of the body. In other words, "life" might just be a store of biological clocks. Their rhythms "are" our lives". These clocks activate programs that keep repeating the same functions at fixed intervals. As they operate and interact with many other such repetitive programs, we live, we act, we behave. Our behavior may simply be the outcome of those numerous programs repeating their mechanical actions. Besides the obvious ones for breathing, heartbeat, seeing, and so forth, there might be repetitive programs for detecting this or that feature of the world, for scanning memory, for learning new knowledge, and so forth, all of them running periodically in the brain over the available information. Perception And Sensation A sensory input undergoes a long series of transformations before leading to a "sensation". Its features are extracted as it is channeled through the brain. Information about its location is isolated early in this process and kept separate from the features. Different regions of cells in the cortex process different features. As the sensory information travels through these regions, each region extracts some feature. For example, one of the most complex sensory inputs is the one that comes from the retina. The component about the location is isolated and routed elsewhere, while information about the sensory input (e.g., the texture, size, color, shape of an image) is still traveling together in one chunk (this produces, for example, the sensation and emotion of the whole image). The location component follows, instead, a completely different path. "What" and "where" are processed separately and in parallel. Concepts And Memories Last but not least, the brain "categorizes". The brain needs to categorize environmental stimuli that are valuable for survival. Every second we are bombarded with millions of sensory stimuli and we slowly force an organization on them, discarding some and retaining others. We turn a chaotic deluge of random stimuli into an ordered flow of patterns. We categorize them in "events", "situations" and "things". The newborn is simply powerless in the face of excess information. We learn slowly to process information and reduce its complexity by organizing our brain. The brain understands what matters by reducing stimuli to concepts, categories. The brain remembers by linking new memories to old memories. The brain, in the face of huge daily sensory stimulation, has a crucial task: understand what matters understand what does not matter remember what will still matter forget what will never matter again Memories are stored in neural activity patterns which are distributed throughout the brain. This system of storage is more versatile and redundant than a "container". It is more redundant because a portion of the brain may be damaged without seriously affecting the overall pattern representing a memory. It is more versatile because it makes it easier to link many different memories. Retrieving a specific memory does not entail finding its location, but turning on its pattern of neural activity. The Dynamic Brain The British zoologist John Young can be credited with starting (in 1964) "selectionist" thinking about the brain. He understood that learning could be the result of the elimination of neural connections (or, better, weakening of synapses). In the 1950s Roger Sperry demonstrated that the brain is pre-wired by the genetic program to deal with some categories and to coordinate some movements. Sperry proved that experience is not enough to shape the brain, whereas Young proved that experience shapes the brain in a Darwinian manner. The essential feature of the brain is that it is a dynamic system, capable of changing very quickly. Even the adult brain "grows". Only about a quarter of the brain is already grown at birth. It is not only quantity, it is mainly quality that is missing. In fact, quantity is taken care of very rapidly: four weeks after conception, an embryo is creating neurons at the fantastic rate of about 500,000 per minute. Six weeks after conception (three months before being born), a fetus has actually more neurons than it will ever have. "Intelligence", though, comes from the synapses. At birth, the brain has fewer synapses than an adult brain. While the brain comes with some synapses pre-wired, many are formed in response to the environment. Synapses proliferate rapidly during the first two years of life. Virtually every event of a child's life leads to the creation of synapses. By far, it is the cortex that witnesses the highest frequency of synaptic creation, while the rest of the brain is largely unchanged after birth. At birth a human brain is much less "finished" than the brains of other animals. Concurrent with the explosion of synapses is a rapid pruning away of those that do not get used. The brain is built through the interplay of genes and experience. The newborn brain comes equipped with a set of genetically based rules that specify how learning takes place. Then the brain is literally shaped by experience (by what is used and what is not used). The infant's brain organizes itself under the influence of waves of "trophic" factors. Such factors are chemicals that promote the growth and interconnections of nerve cells. They are released in waves so that different regions of the brain become connected sequentially. Again, the process is modulated by experience (by what happens to the infant, i.e. by which stimuli enter the infant’s brain). Besides the creation and deletion of synapses, the brain undergoes another phenomenon that shapes its ability to "think": synapses change, again, in response to the environment. Synapses are not simple links between neurons, they are more or less effective in implementing such a link. Donald Hebb's hypothesis, formulated in the late 1940s, is that the basis for neural development lays in a selective strengthening or inhibition of synapses. Synapses that get used are reinforced, while synapses that are not used are inhibited. This dual process molds the structure of the brain in a Darwinian fashion: the more "useful" synapses are the ones that survive. These synaptic changes are the basis for all learning and memory. Hebb had already realized that metabolic change occurs in the brain all the time. The selective strengthening of the synapses causes the brain to organize itself into "cell assemblies", regions of interconnected self-reinforcing sub-nets of neurons that form for long periods of time. These acts of "reinforcing" are more than mere "stimulus-response" pairs: they are reverberating processes that occur over a network of cells. Each assembly represents a fragment of a concept. An assembly may overlap others, so that concepts are naturally linked into larger concepts. Each resonating cell assembly behaves like a rule: triggered by an event, it will fire for a while at a higher rate. Psychological conditioning is ubiquitous in animals because it is a property of individual neurons. Another of Hebb's great intuitions was the "phase sequence". A cell assembly facilitates the formation of another one, normally in conjunction with an external stimulus. A series of chained cell assemblies constitutes a "phase sequence", in which, basically, one thought leads to another. The brain is an evolutionary system: genes determine only its initial configuration, whereas experience molds the brain according to Darwinian principles of selection. Selection Processes Of The Brain Darwinian thinking emphasizes selection over instruction. Some variations are "selected" by the environment over others. Adaptation to the environment is a process of selection. Selection processes are ubiquitous in nature. In 1955 the Danish immunologist Niels Jerne ("The natural selection theory of antibody formation") discovered that a selection process also presides over the immune system. The traditional view of the immune system was that it is capable of manufacturing protein molecules, or "antibodies", in order to neutralize foreign antigens (viruses, bacteria, etc). Jerne and Edelman discovered that, on the contrary, the immune system routinely manufactures all the antibodies it knows how to make. Whenever the body is attacked by foreign antigens, some antibodies (the ones that best "bind" with the invader) are selected and start multiplying rapidly to cope with the invasion. Antibodies are created by the thousands even "before" the body is attacked by anything. An invasion results in a rapid increase in the rate of production of the one antibody that matches the intruder. In a sense, it is the intruder (not the immune system) that decides which antibodies need to multiply. In 1968 Jerne wondered whether a selection process could also account for the mind: do we learn new concepts or are useful concepts chosen by the environment among a pre-existing array of concepts? Do we create a plan of action or is an action selected by the environment from a pre-existing set of actions? Do we think or is a thought selected by the circumstances from a vast pool of possible thoughts? Do we design our mental life, or is our mental life a continuous process of environmental selection of events in our brain? Does our mind manufacture ordered thought or does it manufacture chaotic mental events that the environment orders into thought? Socrates believed that all learning consists in being reminded of what we already know. Jerne, basically, updated Socrates’ idea to Darwinian thinking: every being is equipped with a library of all possible behavior and cognitive life simply consists in finding (within that library) the behavior that best copes with the environmental conditions. The genes encode that "library". They encode information accrued over millions of year of evolution. The mind already knows the solution to all the problems that can occur in the environment in which it evolved over millions of years. Given a problem, it is only a matter of retrieving the appropriate solution. Indirectly, it is the environment that selects what the mind does. And it is the genes that have restricted what the possibilities are for the mind. And the genes too were selected by the environment. Further similarities between the immune system and the neural system were discovered in the following decades. For examples, in 1995 the USA pediatrician Abraham Kupfer showed that immune cells communicate information via synapses in a manner similar to how neural cells communicate information. The information they exchange is presumably about the present dangers within the body. Neural Darwinism Drawing from Jerne’s ideas, in the 1970s the USA biologist Gerald Edelman applied the "selectional" theory of the immune system to the brain. His "Neural Darwinism" is therefore a selectional theory for brain development. Edelman was after a rational explanation for two apparently bizarre facts. First, there is no way that the human genome can specify the whole complex structure of the brain. Second, individual brains are wildly diverse. One would instinctively expect the opposite: all information about the brain should be encoded in DNA and every individual should get pretty much the same brain. Edelman was aware that, before birth, the genetic instructions in each organism provide general constraints for neural development, but they cannot specify the exact location and configuration of each cell. After birth, innate values, i.e. "adaptive cues" (such as "looking for food"), generate behavior and therefore feedback from the environment, which in turns helps "select" the neural configurations that are more suitable for survival. During this on-going process of "learning", the brain develops categories by selectively strengthening or weakening connections between "neural groups". Individual experience "selects" one configuration of neural groups out of all the configurations that are possible. Edelman’s neural groups are a variation on the "cortical columns" of the cortex analyzed by the USA neurologist Vernon Mountcastle in 1957 ("Modality And Topographic Properties Of Single Neurons Of Cat's Somatic Sensory Cortex"). Mountcastle proved that neurons (that perform like functions) are not only organized in horizontal layers, but also in vertical columns. He revealed the modular organization of the brain. Edelman views the functioning of the brain as resulting from a morphological selection of neural groups. Neural groups "compete" to respond to environmental stimuli. That is why each brain is different: its ultimate configuration depends on the stimuli that it encounters during its development. "Adhesion" molecules determine the initial structure of neural groups, the "primary repertory". Experience determines the secondary repertory. Repertories are organized in "maps", each map having a specific neural function. A map is a set of neurons in the brain that has a number of links to a set of receptor cells or to other maps. Maps communicate through parallel bidirectional channels, i.e. through "reentrant" signaling. Reentry is not just feedback because there can be many parallel pathways operating simultaneously. The process of reentrant signaling allows a perceptual categorization of the world, i.e. to relate independent stimuli. This feature enables higher level functions such as memory. Categorization is a process of establishing a relationship between neural maps (through that reentry mechanism). Categories (perceptual categories, such as "red" or "tall") do not exist physically. They are not located anywhere in the brain. Categories are that (on-going) process. Basically, Edelman believes that neural groups are bound to compete and evolve in a Darwinian way, and eventually self-organize as neural maps (purposeful assemblies of neural groups). A further level of organization leads to (pre-linguistic) conceptualization. Conceptualization consists in constructing maps of the brain's own activity, or maps of maps. This process of "global mapping" indirectly retains knowledge of past activity. A concept is not a thing. It is a process. The meaning of something is an on-going, ever-changing process. According to Edelman’s view, brain processes are dynamic and stochastic, whereas the traditional view held the brain to be static and deterministic. Furthermore, the brain is not an "instructional" system but a "selectional" system. It evolves not by changes in a constant set of neurons but by selection of the most valuable neural groups among those that were created at birth. And the elementary unit of this process is not the single neuron, but the neural group. This Darwinian model of the brain explains the non-linearity between the complexity of the genome and that of the brain. The brain is not a direct product of the information contained in the genome. It uses much more information that is available in the genome, i.e. information derived from experience, i.e. indirectly received from the environment. A Brain in Transition There are slight variations on the idea that the brain is a dynamic system. The French neurobiologist Jean-Pierre Changeux believes in "epigenesis by selective stabilization of synapses". In his model too the nervous system makes very large numbers of random multiple connections while, at the same time, external stimuli cause differential elimination of some connections. Again, phenotypic variability (differences among individual brains) is the result of experience. Interestingly, he noticed that phenotypic variability increases with the increase in brain complexity (the simpler the brain of a species the more similar the brains of individual members of that species). The evolutionary advantage of the human species stems from the individual, epigenetic variability in the organization of neurons, which resulted in greater plasticity in adapting to the environment. The USA neurologist Dale Purves, for example, has shown how brain cells are in a perennial state of flux, creating and destroying synapses all the time. Neural activity caused by external stimuli is responsible for the continual growth of the brain, and for sculpting a unique brain anatomy in every individual based on the individual's experience. The British neurologist Semir Zeki argues that perception and comprehension of the world occur simultaneously thanks to reentrant (reciprocal) connections between all the specialized areas of the cerebral cortex. The function of the sensory parts of the cortex is to categorize environmental stimuli. The brain copes with a continually changing environment by focusing on a few unchanging characteristics of objects out of the countless ever-changing bits of information that it receives from those objects. The brain cannot simply absorb information from the environment. It must process it to extract those constant features that represent the physical essence of objects. The brain is basically programmed to make itself as independent as possible from world changes. Patterns And Brains The USA mathematician Ben Goertzel believes that thinking, like life, is a process of evolution by natural selection. In general, Goertzel believes that Darwinism must be supplemented with a theory based on self-organization of complex systems. An organism that, coupled with the other organisms in its environment, generates a large amount of emergent pattern is more likely to survive. Consequently, his model replaces Edelman's neural maps with hierarchical structures that generate emergent pattern. Then neural maps can be viewed as populations that are reproducing sexually and evolving by natural selection. Basically, brain regions are equivalent to ecosystems. And Gould's punctuated equilibrium applies as well to the cognitive development of an individual. Goertzel views minds as sets of patterns interested in recognizing, creating and executing patterns. A mind recognizes patterns in the world, matches them to patterns that are contained within itself, and then creates new patterns both in the world and within itself. The USA physicist Eric Baum argues that mind originates from an "Occam program", a program that stores only the information that is truly needed and in a minimal form. Baum argues that the brain is an unlikely candidate for such a program. The genome, on the other hand, is just that: a program. Baum thus views the genome as the software (or, better, the source code) and the brain as the hardware (or, better, the executable code) that implements his Occam program to deal with environmental patterns, translate them into minimal mind patterns and then enact them as efficient behavioral patterns. And evolution is the software engineer that wrote the program. The USA computer scientist Jeff Hawkins claims to have found the place where this "pattern processing" occurs. Hawkins believes that the columnar structure of the neocortex yields a hierarchical structure of mind (lower levels being closer to raw perception, and higher levels being closer to pure abstraction). At each level the basic form of processing is a combination of matching and creating patterns. Perception, action and cognition are spread throughout this hierarchy of patterns. The brain's function is to store memories as patterns and to make predictions based on such patterns. The brain is fundamentally a forecasting machine, that continuously analyzes the present (current patterns) against the past (stored patterns) in order to predict the future. The USA neurologist Walter Freeman believes that the brain creates patterns that have little or nothing to do with the real world: they "create" a world that is consistent and complete, based on (basically) computational efficiency, not on accuracy. These scientists place different emphasis on "how" the mind decides to build patterns. Does it use a goal-oriented approach (makes predictions that are useful for its goals), does it use a genetic-oriented approach (makes predictions that match its genetic repertory), or does it use a computational approach (makes the predictions that reduce the complexity of the world)? The implementation in the brain of this prediction machine is the link between neural processes and symbolic processing: neural processes ultimately constitute the vehicle to create and manipulate symbols. Presumably, this function involves a massive use of some form of Hebbian learning, leading from disjointed instances to more and more organic and abstract representations. Thus generalization and metaphorical thinking are the fundamental basis of cognition. The Selectional Mind The USA neurophysiologist Michael Gazzaniga extended Jerne's ideas to prove that a selection process also governs higher mental functions such as language and reasoning. Gazzaniga agrees with Edelman that, during growth, selection processes determine how a brain is wired for adult functioning. Brains are born with a vast number of pre-wired circuits, which nonetheless offer many alternative options for development; and experience determines which of these pre-existing brain circuits are used. Many possible connections can be made, but only some are selected by experience. The mind is shaped by the environment; but the environment can only shape it as far as genetically-fixed parameters allow. It is more appropriate to say that the environment "selects" from the possible outcomes. Neurons exist because it was written in the genetic code. They perform their function no matter what. It is the interaction with the environment that will prefer some neurons over others. But, ultimately, the neurons were already there. Gazzaniga differs from Edelman in emphasizing the importance of innate structures. Learning consists in discovering already built-in capabilities. The phenomenal rate of learning in children can be explained by admitting that children already "know". What they are learning is what is selected through interaction with the environment. Noam Chomsky's universal grammar is an example. Children quickly learn a language because linguistic knowledge is present in their brain at birth and all their brains have to do is pick what is consistent with the specific language spoken around them. All humans are equipped from birth with some general features that allow for intelligent behavior in our world. Experience (i.e., interaction with the environment) will decide how that behavior will materialize. Convergence Zones A new paradigm was introduced in the 1980s by the Portuguese biologist Antonio Damasio. When an image enters the brain via the visual cortex, it is channeled through "convergence zones" in the brain until it is identified. Each convergence zone handles a category of objects (faces, animals, trees, etc.) A convergence zone does not store permanent memories of words and concepts but helps reconstructing them. A convergence zone is not a "store" of information, but an "agent" capable of decoding a signal (of reconstructing information). In this function, they resemble an "index" that can be used to organize a perception. There is no specialized region of the brain that encodes an event (a memory). The various features of a perception are held in the places where they were analyzed (somewhere in the cortex). The convergence zones are different regions of brain that manage the task of connecting those fragments of perceptions and of connecting them to previous "memories". Convergent zones also produce output. If convergence zones reactivate simultaneously fragments that used to be connected when they were first "memorized", then we "remember" the event represented by the set of those fragments. Once an image has been identified, an acoustic pattern corresponding to the image is constructed by another area of the brain. Finally an "articulatory" pattern is constructed so that the word that the image represents can be spoken. There are about twenty known categories that the brain uses to organize knowledge: fruits/vegetables, plants, animals, body parts, colors, numbers, letters, nouns, verbs, proper names, faces, facial expressions, emotions, sounds. Convergence zones exist at several levels. A convergence zone may be responsible for linking the attributes of a face, while another may be responsible for linking the face to other concepts or faces. Convergence zones form a hierarchy of specialized agents (although they are connected in a network-like fashion). Each convergence zone is the focal point for the integration of disparate features. Convergence zones "bind" together objects, concepts and events at different levels of cognition. Convergence zones behave like indexes that draw information from other areas of the brain. The memory of something is stored in bits at the back of the brain (near the gateways of the senses): features are recognized and combined and an index of these features is formed and stored. When the brain needs to bring back the memory of something, it will follow the instructions in that index, recover all the features and link them to other associated categories. As information is processed, moving from station to station through the brain, each station creates new connections reaching back to the earlier levels of processing. Convergence zones enable the brain to work in reverse. Phantoms in the Brain By analyzing different kinds of brain damage, and the feelings associated with phantom limbs (people with missing limbs can still feel pain in those non-existent limbs), the Indian neurologist Vilayanur Ramachandran concluded that the brain constructs cognitive maps that are, basically, plausible interpretations of the world. It is those maps that cause all mental life, starting from perception itself. For example, the limb is no longer there, but its representation in the brain is still there, and thus the person feels it as if it were still there. Whether it is truly there or not is negligible compared with the fact that it is represented in the brain. By generalization all mental life could be "phantom", because that is a general behavior of the brain. All sensory experience is an illusion. All feelings are illusions. Even the self consists of an illusion, largely constructed out of interactions with others. The brain creates these representations of different kinds (from representations of limbs to representations of the I) and then believes that they truly exist and they get associated with feelings. (Thus the solution to the pain caused by a phantom limb would be to induce the brain to believe that the phantom limb does not exist anymore, i.e. to remove the representation of that limb in the brain). In a sense, the entire body is a "phantom limb": the brain constructs its existence and then "feels" it. Mirror Neurons The Italian neurologist Giacomo Rizzolatti discovered ("Action Recognition in the Premotor Cortex", 1996) that the brain of primates uses "mirror" neurons to represent what others are doing. De facto, my brain contains a representation of what someone else is doing, and that representation helps me "understand" what the other person is doing, for example her intention and her emotions. We effortlessly understand the intention and emotion of others not because we carry out complex reasoning procedures about their actions but because their intentions and emotions are physically reproduced inside our own brain. In fact, a brain only needs to see the beginning of an action by another person in order to guess the intention of it: based on the context, the mirror neurons instantly reproduce the brain state of the other person and therefore help to understand what the other person is trying to do and what will happen next. These mirror neurons are widespread in the cortex of primates (not only of humans). These mirror neurons fire both when the action is performed and when the action is observed in other individuals. Ramachandran ("Mirror Neurons and Imitation Learning", 2000) subsequently speculated that mirror neurons may be crucial in learning and understanding language. Neural Communication There are indications that communication within the brain may involve a different kind of paradigm from the one employed by human-built machines. We tend to think of communication between parts as a signal that travels from a point in the system to another point in the system. In the brain, though, messages do not seem to carry meaning (per se). The Brasilian neurologist Sidarta Ribeiro ("Global Forebrain Dynamics Predict Rat Behavioral States And Their Transitions", 2004) argued that communication is carried out via patterns of activity that involve entire regions. It is the pattern of activity that carries and delivers meaning. By the same token, the Indian neurologist Mayank Mehta ("Role of Rhythms in Facilitating Short-term Memory", 2005) claimed that the neocortex communicates with the hippocampus for the transfer of long-term memories via synchronized patterns of activity (a rhythmic pattern of the excitatory cells in the neocortex corresponds to a rhythmic pattern of the inhibitory neurons in the hippocampus). Different regions of the brain communicate by synchronized firing of neurons (as opposed to a linear transmission of signals from neuron to neuron to neuron). The Free Will of the Brain The traditional view of the brain is that, fundamentally, it serves the purpose of "reacting" to what happens in the environment. As the body encounters new situations, the brain decides what the body must do to cope with them. The traditional view is that the brain is activated by the sensorial data and in turns activates the external organs of the body to generate movement. This view was challenged by the Colombian neurologist Rodolfo Llinas. First of all, Llinas does not believe that the neuron is simply a switch: Llinas ascribes a personality to each single neuron. They don’t simply react to stimuli, they are active all the time, generating patterns of behavior all the time. Second, Llinas considers the brain a "prediction machine". Organisms that need to move also need to represent the world and make predictions on what is going to happen. Therefore they need a brain. However, his opinion is that, once endowed with a brain, an organism has only limited control of it. Neurons are always active, even when there are no inputs from the external world. Neurons operate at their own pace, regardless of the pace of information coming in from the outside. A sort of rhythmic system controls their work. They produce a repertory of possible actions. The circumstances "select" which specific action is enacted. For example, the motion of cerebellum neurons results in body movements if the conditions are appropriate (the cerebellum is the part of the brain that controls movement). But, in a sense, the neurons are telling the body to move even when the body is not moving and before the body started moving. Movement is not reactive: it is active and automatic. The environment, in a sense, selects which movement the body will actually perform, but at that point in time the brain may have been ready to perform many other movements. "I" am a consequence of my brain thinking. My brain is thinking and the environment is deciding what it is thinking, and "I" only exist after the fact (my mental life only exists after the fact, my conscious I, my illusion of being a being, only exists after the fact). I don't think, I simply have the illusion of thinking. In reality the brain is thinking independently from my will, its thoughts shaped by experience, and then, after they have been thought and selected by the environment, I can experience them. Ultimately, the environment is thinking my thoughts! The Advent of the Brain: Encephalization The history of the brain is the history of the nervous system. Multi-cellular organisms eventually developed the ability to control their cells. Each cell had its own internal mechanism of control, and somehow was capable of mediating with the other cells. The nervous system is made of cells that mediate the need of the cells of the body. This function was evolutionarily useful and therefore persisted and evolved. It presumably evolved both in quantity and in quality: more and more nervous tissues would coordinate the movements of the organism, and more and more processing would be performed based on performance. Eventually the nervous system started building abstractions of controls, the equivalent of "representing" the body and its interaction with the environment. At this point it made sense that the nervous system became "headquartered" in one specific place, rather than being spread throughout the body. "Encephalization" is the name given by the British neurologist Hughlings Jackson to the process whereby the nervous system of living organisms grew in size and importance especially in the head. What used to be a distributed system of control then became a centralized system of control. In mammalians, more and more centralized tasks were created via the newly born cerebral cortex. The modern brain was born. Multiple brains: the Advent of Cognition Because higher functions of the brain tend to be generated by the regions (such as the cortex) that appeared in more recent species (such as us), it is likely that the human brain has accumulated functions and structures over the ages. Hughlings Jackson also noticed that a loss of brain function is often compensated by a gain in another brain function, and concluded that an evolutionarily "older" brain takes over whenever the "newer" brain is disabled: the older brain is still there, even though a newer brain grew on top of it. Today's brain basically "summarizes" its evolutionary history: its structure and functioning contain its predecessors. Older creatures tend to have no central nervous system, but rather a loose affiliation of nerve fibers. As we move down the genealogical tree, that chaotic form of communication among cells gets disciplined through a more and more centralized system that performs more and more sophisticated processing of the signals. Hot-blooded animals also need to control temperature and require a more complex control mechanism. Earlier mammals exhibit a forebrain and later mammals developed the cerebral hemispheres. Throughout this evolution of more and more refined nervous systems, the earlier ones remained around. The primitive forebrain is still part of the human brain (and it accounts for a lot of our emotional life). Loose networks of nerve fibers still control organs around the body, and often the brain cannot override them. And so forth. One can recognize within the human brain the facsimile brains of amoebas, insects, worms, etc. The USA biologist Philip Lieberman proposed that the brain consisted of a set of specialized circuits that evolved independently at different times. Many specialized units work together in different circuits (the same unit can work in many circuits). The overall circuitry reflects the evolutionary history of the brain, with units that adapted to serve a different purpose from their original one. For example, rapid vocal communication (as in "speaking) is actually responsible for the evolution of the human brain, and not the other way around. Lieberman's "circuit model" was derived from the model of the brain worked out by the USA physician Norman Geschwind ("Disconnexion Syndromes In Animals And Man", 1965, the manifesto of behavioral neurology) in order to explain aphasia, a model that reconciled localization and connectionism. Besides language, another unique trait of the human race (and therefore of the human brain) is the moral code, in particular altruism. This would also be a relatively recent development, and presupposes circuitry for language and cognition. Microgenesis "Microgenesis" is an extreme version of this view. The idea, originally advanced by the USA psychologist Jason Brown, is that mental process recapitulates evolutionary process. Microgenesis assumes that the structure of perceptions, concepts and actions (and mental states in general) is not based on representations but on processing stages that last over a micro-time, propagate "bottom-up", and are not conscious. A representation is but a section of a processing continuum. Mind is not the final representation, it is the very series of processing stages. Earlier processing stages remain part of the final stage just like a child's early stages of development persist as subconscious themes in the adult's cognitive life. Microgenesis means that at every point in time the brain revisits the very steps that made it evolve from a simple stimulus-response mechanism to a complex control system. Every single line of reasoning goes through all the layers, starting with the primitive emotional reactions that are common to many animals and ending with the sophisticated logical processing that is unique to humans. Microgenesis is the equivalent for micro-times of ontogenesis (growth of the individual) and phylogenesis (evolution of species). They are the expression of the same general process over different time scales. Microgenesis is sort of instantaneous evolution. The theory implies that symptoms of brain damage represent normal stages in the cognitive life at microscopic level. Therefore they can be used to reconstruct cognitive life. For example, Brown used this technique to reconstruct the way language is produced and understood. The Triune Brain The USA neurologist Paul MacLean popularized the notion that the human head contains not one but three brains: a "triune" brain. Like the layers of an archeological site, each brain corresponds to a different stage of evolution. Each brain is connected to the other two, but each operates individually with a distinct "personality". The neocortex does not control the rest of the brain: all three parts interact, although it is true that the neocortex interacts in a more "cognitive" manner. But the "brain" that interacts in a more "instinctive" manner can be as dominant and even more. And ditto for the "emotional" one. The oldest of the three brains, the "reptilian" brain, is a system that has changed little from reptiles to mammals and to humans. This "brain" comprises the brain stem and the cerebellum. It is responsible for species-specific behavior: instinctive behavior such as self-preservation and aggression. The cerebellum and the brainstem constitute virtually the entire brain of reptiles. The most basic life-sustaining processes of the body, such as respiration, heartbeat and sleep, are controlled by the brainstem. More precisely, the brainstem is the brain's connection with the autonomic nervous system, the part of the nervous system that regulates functions such as heartbeat, breathing, etc. that do not require conscious control. It is always active, even when we sleep. It endlessly repeats the same patterns over and over again, mechanically. It does not change, it does not learn. In ancient species this system was basically most of the brain, and limbs and organs were controlled locally. Most mammals share with us the limbic system, which MacLean believes was born after the reptilian system and was simply added to it. The earliest mammals had a brain that was basically the reptilian brain plus the limbic system. MacLean therefore believes this to be the old mammalian (or "paleo-mammalian") brain. The limbic system contains the hippocampus, the thalamus and the amygdala, which are considered responsible for emotions and emotional instincts (behaviors related to food, sex and competition). These emotions are functional to the survival of the individual and of the species. This system is capable of learning, because it contains "affective" memories, i.e. emotion-laden memories. Ultimately, the limbic system is about "pain" and "pleasure": avoiding pain and repeating pleasure. The neo-cortex is the main brain of the primates, which are among the latest mammals to appear. All animals have a neo-cortex but only in primates it is so relevant: most animals without a neocortex would behave normally. This "neo-mammalian" brain is responsible for higher cognitive functions such as language and reasoning. The oldest of the three brains is located at the bottom and to the back. The newest sits on top and to the front. They all complement each other to produce what we consider human behavior. Each is an autonomous unit that could exist without the others. The elegance of MacLean's model is that it neatly separates mechanical behavior, emotional behavior and rational behavior. It shows how they arose chronologically and, indirectly, for what purpose. And it shows how they coexist and complement each other. They constitute three steps towards human "intelligence". The USA psychologist Anthony Stevens related these three brains to Jung’s division of the mind into a conscious, un unconscious and a collective unconscious, the collective unconscious being the oldest one and therefore assigned to the reptilian brain. An Olfactory Brain The USA neuroscientist Rhawn Joseph argued that the human brain still contains parts that were used by animals that lived hundreds of million of years ago. In other words, we share parts of the brain of many other animals, and, ultimately, one can say that all animals are "linked" by the "collectively shared unconscious" Joseph calls the human body a "living museum" because it contains so many remnants of ancient organs. This is also visible in language: while we have developed sophisticated spoken languages, we still use gestures, that are presumably an archaic form of communication. Old and new languages coexist. We often communicate unconsciously to other beings precisely because we still have, like it or not, the old languages. For example, a facial expression is enough to communicate our state of mind. Neurons (nerve cells) first appeared 700 million years ago. When neurons got connected, the first brain was born. Joseph believes that the first major grouping of neurons occurred among olfactory cells, that originally may have been external cells. Eventually they migrated inside the body and created am olfactory lobe. Later, a similar fate turned visual cells into the visual lobe. The growth of these two lobes over evolutionary time eventually yielded the brain as we know it (the two hemispheres). The olfactory lobe also evolved into the limbic lobe, that still controls many of the "instinctive" activities (in both humans and other animals). The cells of the limbic lobe created more and more layers, and eventually created the cortex. Thus the fundamental structure of the modern human brain evolved from the olfactory lobe. Among the various forms of communication that are crucial to our understanding of the world, Joseph believes that odors play an important role. The nose contains the most exposed (unprotected) neurons of the human body. The mucosa of the nose is directly connected to the hippocampus and the amygdala, which are instrumental in creating memories. It is likely that living beings developed the ability to analyze chemicals (odors) in order to understand changes in the environment and to sense other beings (in fact, our bodies still excrete odor-generating chemicals from the skin). Odors, after all, control sex and aggression and many other basic activities of most species. The Purpose Of A Brain The British neurologist John Young once argued that "the most important thing of living beings is that they remain alive". A stable state (homeostasis) is what they aim for. Young claims that homeostasis is precisely the job of the brain, the most delicate job of all. Homeostasis requires appropriate responses to the environment, responses whose goal is to keep the state stable. The brain's job is to maintain homeostasis through the selection of appropriate responses. The brain is the computer of a "homeostat". This computer uses a memory, or, better, two memories. One memory is the one created by evolution and inherited at birth, that contains knowledge that can be used in many commonly-occurring situations, whereas the other memory (the one we call "memory") is the one that contains up-to-date knowledge about the outcome of actions during our lifetime. What these two memories do is to collect information (over generations or over a lifetime) that helps the brain define the desired state and maintain that stable state. The Heat Engine Of The Body The Spanish neurologist Francisco Mora introduced a simple vision for what brains do for us: they regulate our temperature. From the beginning life was capable of reacting to temperature: even the earliest unicellular organisms must have been capable of sensing heat and cold. Heat, after all, was the primeval source of energy for living organisms. These organisms required heat to survive and the main source of heat came from the environment. The progenitors of the living cell, the "protocells", were probably units of energy conversion, converting heat into motion, just like a heat engine. In 1995 the Dutch chemist Anthonie Mueller, the proponent of "thermosynthesis", showed that such systems could form spontaneously in the primordial conditions of the Earth. If they survived, these organisms must have developed a way to react to positive and negative stimuli, such as correct or excessive amount of heat. The early nervous system were assemblies made of cells already capable of sensing and reacting to temperature. Proof is that all known organisms, including unicellular ones, are capable of avoiding adverse environmental temperatures. In other words, throughout evolution all organisms were capable of sensing external temperature. Mora speculates that during the transition from water to land (from stable temperature to wildly variable temperature) the nervous system must have learned to control body temperature. Nocturnal animals must have developed also a means to overcome the loss of environmental heat and produce heat internally. And the autonomic control of temperature was born. This feature allowed the evolution from cold-blooded animals (animals whose temperature fluctuates with the temperature of the environment, whose only sources of heat are external sources) to warm-blooded animals (animals that maintain constant body temperature by producing heat internally). Cold-blooded animals are dependent on environmental heat: when ambient temperature rises, they are active and seek food; when ambient temperature decreases, their motor activity slows down. Warm-blooded animals overcame this limitation thanks to that self-regulating feature, thanks to the ability of producing heat internally when heat from outside is not enough. And they freed themselves from their habitat: they were capable of changing habitat because they were capable of maintaining their body temperature regardless of changes in the external supply of heat. A very efficient self-regulating heat engine that maintains temperature constant opens up new opportunities for evolution: one organ that benefited was the brain, that could grow to its actual size and complexity. If it didn't have an adequate supply of energy, the brain would not be capable of performing the tasks it performs. A hot organ is required for thinking. Modern mammals, who have the highest demand for internal production of heat, regulate temperature through a whole system of thermostats, not just one. Experiments have proved that mammals have not one but many centers of control of body temperature: in the spinal cord, in the brainstem, in the limbic system and mainly in the hypothalamus. Rather than one point of control, this is more like a complex system, that peaks in the hypothalamus. It is a very accurate system: humans can survive only in a narrow temperature range (a few degrees below or over 37 degrees a human body becomes a dead body). Why regulate at 37 degrees instead of, say, 20? It turns out that 37 degrees is the ideal temperature for balancing heat production and heat loss. Ultimately, the brain is responsible for maintaining a constant temperature, the very constant temperature that allows the brain to function. The Solipsistic Brain The USA neurophysiologist Walter Freeman discovered that the neural activity due to sensory stimuli disappears in the cortex and in lieu of it an apparently unrelated pattern appears, as if the brain created its own version of what happens in the world. Most of the sensory input is basically wasted. Freeman came to believe that "a form of epistemological solipsism isolates brains from the world". Each brain creates its own world, which is internally consistent and complete. Contrary to a popular paradigm, perception does not consist of information reception, processing, storage, and recall. Perception is the creation of meaning, a very "subjective" process. How do "solipsistic" brains communicate? Brains communicate, basically, by "unlearning": unlearning is a process by which a brain must give up its beliefs and learn new ones through "socially cooperative" actions. Freeman believes that brains have evolved primarily as organs of social cooperation, and originally they started communicating for sexual reproduction. He retraces the story of socialization, from the early formation of pair bonds and tribal groups and identifies music, dance, and sexually based rituals as the means by which meanings in the brains were shared. Since awareness follows brain activity by about half a second, Freeman believes that awareness is the perception of the brain's working, and not the other way around. The Origins Of Brains The anthropological record tells the story of a dramatic increase in brain size that happened over a relatively short period of time. Humans became "intelligent" suddenly and very rapidly. Many scientists and philosophers believe that this rapid increase in brain size must have been driven by a self-amplifying process. The typical self-amplifying processes are positive feedback loops, in which growth is triggered by growth itself, and there is nothing to stop the growth. The state of the system is out of control. (In negative-feedback systems, such as a furnace for heating a house, there is a control mechanism, e.g. the thermostat. that controls growth for the purpose of maintaining a desired state). A positive feedback would explain the rapid evolution of the brain. The British philosopher Nicholas Humphrey argues that positive feedback may have come from pressure for "social intelligence", the need to communicate and share with other members of our species. The British biologist Ronald Fisher thought that sexual selection was a form of positive feedback, and this thesis was also defended by the USA psychologist Geoffrey Miller. Are Colors More Real Than Pain? We perceive the world in at least two different ways: one is the sensations that come from the senses (seeing, smelling, touching, hearing, tasting) and one is the feelings that somehow are generated in response to things that are happening to our body (pain, pleasure, hunger, hate, fear, etc). Colors and shapes seem to be direct perceptions of the world out there, whereas pain seems to be the fictitious outcome of a process in our brain. It turns out that colors and shapes and sounds and so forth are not shared by all living organisms. As a matter of fact, every species has its own "sensations" that are different from other species. Some animals see the world in three dimensions, but some see it in two dimensions. Some see colors, and some do not. Other species may see "things" that we don't see. Their eyes are different and their brains are different. There is no evidence that what we "see" is what is out there (rather than, say, what the frog sees). Colors and shapes and sounds and so forth are devices to "map" the outside world so that our body can deal with it in an efficient way. Once we build such a "map" of the outside world, we can, for example, move without hitting solid things and grab things that we want to eat. Emotions are more of the same, but at a more primitive level. They direct our behavior, but they don't require a representation of the outside world. They just tell us "don't do that" or "do that". While the ability to see and hear and smell seem to be more primitive than the emotions of pain and pleasure, it is likely to be the opposite. What is more important for survival? To be able to map the world into objects of such a shape and such a color, or to be able to find food and detect danger in a millisecond? The early multicellular organisms were probably incapable of any significant mapping of the world around them. They were capable, though, of avoiding dangerous places and moving towards more promising places. They were equipped with simple cells (the progenitors of today's nervous system) that could react to the temperature and to the chemical composition of the surroundings and simply move away or move towards them. If floating in a pond, those cells would have been able to realize that the temperature was reaching a dangerous level (say, because of a nearby lava flow) and therefore cause movement in the opposite direction. This progenitor of "pain" was much more relevant than assigning a shape or a color to the pond and the lava flow. The ability to map the world through the senses was a later development, one that provided organisms with an even more sophisticated survival strategy. Brains are for Traveling and Chatting What are brains for? Why a rock or a plant can be what it is without a brain, while an animal cannot exist without a brain? What is the unique feature that a brain enables? One property of living beings is striking. Plants, which do not move, do not have brains. They too grow and they too need to coordinate their growth, but they don't seem to need a brain to do so. Mammals and birds appear to have the most sophisticated ability to move. Mammals and birds have the most sophisticated brains. The brains of snakes, frogs and fish appear to be simpler, and it turns out that these creatures do not move in as creative a way as mammals and birds. Invertebrates have even simpler brains and their movements are even more basic. Birds and mammals can move very long distances, over huge territories, dealing with a broad spectrum of ecological changes, even crossing oceans and continents, and they can move in a virtually endless variety of ways. Other animals seem to be more limited both in distance and in the degrees of freedom of their movements. Another property of living beings stands out. The biggest brain (about 10 kg) belongs to the sperm whale. The record for brain size compared with body mass belongs to the squirrel monkey (5% of the body weight, versus 2% for humans). Some birds too have a higher "brain percentage" than ours (the sparrow is a close second to the squirrel monkey). Two rules seem to tell something about the reasons for larger brains: 1. Bodies of warm-blooded animals consume ten times more energy so brains can be ten times bigger. 2. Species that live in large social groups have the largest brains (the squirrel monkey lives in bands of hundreds of individuals). Beyond the brain How the brain came to be is a long and convoluted story. The brain is made of several regions that evolved at different times and probably for different purposes, and eventually got locked together in the same organ. It is likely that these different circuits had to adapt to each other and to the other organs of the body. Ultimately, the brain had to make sense in the context of itself and of the whole body. What didn't fit in the overall picture was probably fixed by natural selection. The brain is a Darwinian system, within which the concepts of competition and self-organization are much more important than the ones of design or organization. The brain is a battlefield. Of all possible million configurations at each point in time one is chosen that best fits our experience. Far from being a well-determined logical system, the brain is a chaotic system of trial and error. It is all the more amazing that I can say "I", because my "I", if it is due to my brain, changes all the time, and I have no control over the way my "I" changes: it is experience, not my free will, that selects which connections will get stronger and which ones will die out. I have no more control on the evolution of my thoughts than I have on the evolution of my species. Over the 19th century we learned to admit our fundamental inability to affect the evolution of our species, and of life in general. A far more powerful force, natural selection, takes care of that. We are simply pawns, created more or less by accident, and doomed to be eventually replaced by other pawns in this eccentric game of life. Over the 20th century we began to realize that we are also powerless to affect the evolution of our brain, of our own selves. We, at the level of the individual, seem to be in the hands of far more powerful forces that mold our brains regardless of what we would like to be. Ultimately, our brain is not "ours". Consciousness is the mysterious entity that somehow enters the picture through the very same brain that we discovered is outside our sphere of influence but that at the same time somehow, we believe, grants us a degree of freedom in thinking, feeling and, ultimately, being what we are. Further Reading Baum Eric: WHAT IS THOUGHT? (MIT Press, 2004) Brown, Jason: THE LIFE OF THE MIND (Lawrence Erlbaum, 1988) Changeux, Jean-Pierre: NEURONAL MAN (Pantheon, 1985) Changeux, Jean-Pierre: ORIGINS OF THE HUMAN BRAIN (Oxford University Press, 1995) Churchland, Paul: ENGINE OF REASON (MIT Press, 1995) Damasio, Antonio: DESCARTES' ERROR (G.P. Putnam's Sons, 1995) Edelman, Gerald: NEURAL DARWINISM (Basic, 1987) Eichenbaum, Howard: COGNITIVE NEUROSCIENCE OF MEMORY (Oxford Univ Press, 2002) Freeman, Walter: SOCIETIES OF BRAINS (Erlbaum, 1995) Gazzaniga, Michael & LeDoux Joseph: INTEGRATED MIND (Plenum Press, 1978) Gisolfi, Carl & Mora Francisco: THE HOT BRAIN (MIT Press, 2000) Goertzel Ben: THE STRUCTURE OF INTELLIGENCE (1993) Goertzel, Ben: THE EVOLVING MIND (Gordon & Breach, 1993) Goldstein, Kurt: THE ORGANISM: A HOLISTIC APPROACH TO BIOLOGY (USA Book, 1939) Hawkins Jeff: ON INTELLIGENCE (2004) Hebb, Donald: ESSAY ON MIND (Lawrence Erlbaum, 1980) Ivry, Richard & Robertson, Lynn: THE TWO SIDES OF PERCEPTION (MIT Press, 1998) Hebb, Donald: THE ORGANIZATION OF BEHAVIOR (John Wiley, 1949) Hull, Clark: PRINCIPLES OF BEHAVIOR (Appleton-Century-Crofts, 1943) James, William: THE PRINCIPLES OF PSYCHOLOGY (1890) Jerne, Niels: THE NATURAL-SELECTION THEORY OF ANTIBODY (1955) Joseph, Rhawn: NAKED NEURON (Plenum, 1993) Koehler, Wolfgang: INTELLIGENSPRUEFUNGEN AM MENSCHENAFFEN (1925) Lashley, Karl: BRAIN MECHANISMS AND INTELLIGENCE (Dover, 1963) Lavine, Robert: NEUROPHYSIOLOGY (Collamore, 1983) Lieberman, Philip: UNIQUELY HUMAN (Harvard Univ Press, 1992) Llinas, Rodolfo & Churchland Patricia: THE MIND-BRAIN CONTINUUM (MIT Press, 1996) MacLean, Paul: THE TRIUNE BRAIN IN EVOLUTION (Plenum Press, 1990) Miller, Geoffrey: THE MATING MIND (Doubleday, 2000) Purves, Dale: NEURAL ACTIVITY AND THE GROWTH OF THE BRAIN (Cambridge Univ Press, 1994) Ramachandran, Vilayanur & Blakeslee, Sandra: PHANTOMS IN THE BRAIN (Morrow, 1998) Skinner, Burrhus: BEHAVIOR OF ORGANISMS (1938) Thorndike Edward: ANIMAL INTELLIGENCE (1911) Underwood Geoffrey: OXFORD GUIDE TO THE MIND (Oxford Univ Press, 2000) Valiant, Leslie: CIRCUITS OF THE MIND (Oxford University Press, 1994) Ramachandran, Vilayanur & Blakeslee, Sandra: PHANTOMS IN THE BRAIN (Morrow, 1998) Young, John: A MODEL OF THE BRAIN (Clarendon Press, 1964) Zeki, Semir: A VISION OF THE BRAIN (Blackwell, 1993)