The Nature of Consciousness

Piero Scaruffi

(Copyright © 2013 Piero Scaruffi | Legal restrictions )
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These are excerpts and elaborations from my book "The Nature of Consciousness"

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 mechanical functions, but even more vital than the higher ones.

 


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