Piero Scaruffi(Copyright © 2013 Piero Scaruffi | Legal restrictions )
These are excerpts and elaborations from my book "The Nature of Consciousness"
The Colombian neurophysiologist Rodolfo Llinas has interpreted these findings as a scanning system that sweeps across all regions of the brain every 25 milliseconds (40 times a second). The region of the brain containing the information about a sensation constitutes the "context" of an instance of conscious experience. The 40Hz oscillation provides the "binding" of such content into a unified cognitive act.
This wave of nerve pulses is sent out from the thalamus and triggers all the synchronized cells in the cerebral cortex that are recording sensory information. The cells then fire a coherent wave of messages back to the thalamus. Only cortex cells that are active at that moment respond to the request from the thalamus. Consciousness originates from this loop between thalamus and cortex, from the constant interaction between them. Consciousness is generated by the dialogue (or "resonating activity") between thalamus and cortex.
Consciousness is simply a particular case of the way the brain works. Other brain regions have their own temporal binding code. The motor system, for example, works at 10 cycles per second (which means that movements only occur ten times a second, not continuously). Every function is controlled by a rhythmic system that occurs automatically, regardless of what is happening to the body. Consciousness happens to be the phenomenon generated by that specific rhythmic system that operates on the brain itself.
Besides the 40-cycle-per-second, the brain has a number of natural oscillatory states: at 2 cycles per second it is sleeping. One of the brain's functions is to create images: at 2 cycles per second it creates dreams; at 40 cycles per second it creates images that represent the outside world as perceived by the senses.
In other words, the brain is always working independently of what is happening outside: during sleep, i.e. in the absence of sensorial data, that work is called “dreaming”; during the day, in the presence of sensorial data, it is called thought. The difference is that the brain’s automatic dreaming is conditioned by the senses: when the senses are bombarded by external stimuli, the brain can generate only some types of thought, just like the body can generate only some types of movement. At every instant, the brain is dealing with both reality and fantasy." A person's waking life is a dream modulated by the senses".
The US neuroscientist Paul Churchland provided a detailed description of how the brain perceives sensory input (in particular vision) through what he calls "vector coding". He claims that consciousness must be based on a "recurrent" network, and Koch's 40 Hz oscillation in the cortex is a convenient candidate for a brain-wide recurrent network. That brain-wide recurrent network would be able to unify the distinct senses in one consciousness.
In this sense, therefore, consciousness does not require language, and non-linguistic animals can be conscious too. Consciousness is biological, not social (its contents may be social, such as language).
In general, dynamic processes can be coherent in one frequency band while being incoherent in another band. Resonance is the capacity of a system to respond selectively to stimuli in narrow frequency bands. Television sets and radio sets allow the viewer/listener to pick the resonant frequency (i.e. the broadcast). Once that is done, the tv set responds only to inputs (i.e. shows only the broadcasts) at that frequency. The tv set becomes part of a broader network at that frequency, while remaining totally isolated at other frequencies.
The US neurophysiologist Paul Nunez thinks that something similar takes place among neural groups: some can be bound by resonance at some frequency while, at the same time, operating independently at other frequencies. This means, in particular, that two cortical groups can be highly coherent (i.e. strongly correlated) at one frequency while being weakly coherent (i.e. weakly correlated) at another frequency.
A general property of oscillators is that weakly coupled oscillators can interact strongly when they produce appropriate resonant frequencies. The US biophysicist Bill Baird had already shown how oscillatory neural networks can account for pattern formation and recognition ("Nonlinear dynamics of pattern formation and pattern recognition in the rabbit olfactory bulb", 1986). The synchronization of oscillating networks was then the object of the research by the US mathematicians Frank Hoppensteadt and Eugene Izhikevich ("Synaptic organizations and dynamical properties of weakly connected neural oscillators", 1996).
Nunez synthesizes these studies as showing that neural groups can use rhythmic activity to communicate selectively even to groups to which they are not directly connected. It means that neural groups that are not adjacent can collaborate in performing a mental task.
Brain regions are functionally isolated at some frequencies while being functionally integrated at some other frequencies. Hence the "binding" that yields consciousness takes place both in space and in time. Consciousness is due to both local and nonlocal connections.
In general, complex adaptive systems (such as the brain) can operate over a broad range of isolation or integration. At one extreme there is functional isolation of the subsystems; at the other extreme there is global coherence. The brain, in particular, is both a set of subsystems with minimal communication (when it operates in "functional isolation" mode) and a whole that is globally coherent. Neurotransmitters can move the brain along that continuum, from granular assembly of functionally isolated subsystems to highly integrated globally coherent whole. In fact, Nunez thinks that a balanced mental state is a balanced compromise between the two extremes; and that mental diseases can be explained as overcorrelated or undercorrelated states.
Nunez notes that when one undergoes anesthesia (i.e. when "thinking" is vastly reduced), local differences tend to disappear. His interpretation is that the transition from intense mental activity to minimal mental activity corresponds to a transition from local to global neural activity.
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