Piero Scaruffi(Copyright © 2013 Piero Scaruffi | Legal restrictions )
These are excerpts and elaborations from my book "The Nature of Consciousness"
Time-Based Binding Abstracted
The US biologist Charles Gray then hypothesized (“Synchronous Oscillations in Neuronal Systems“, 1994) that the memory of something is generated by a stream of oscillating networks. Separate brain regions (corresponding to different categories of features) send out nervous impulses at the same frequency and the perception of an object is created by the superimposed oscillation. The brain uses frequency as a means to integrate separate parts of a perception. In this way the limited capacity of the brain can handle the overwhelming amount of objects that the world contains (the number of objects we see in a lifetime exceeds the number of neurons in the brain that would be needed to store them as images).
This theory is compatible with both Damasio's and Edelman's theories, as they all posit some type of "synchrony" for consciousness of something to emerge. According to these theories, it is time, not space, that binds.
Time-based binding almost marks a revival of “gestalt" psychology (the oscillation is, for practical purposes, a gestalt).
The German neurophysiologist Pascal Fries showed that neuronal communication is implemented via neuronal synchronization ("A Mechanism for Cognitive Dynamics", 2005).
The Italian psychiatrist Giulio Tononi, however, noticed that one would therefore expect brain wave synchronization to increase with degrees of consciousness. Instead, when people lose consciousness, brain waves become more (not less) synchronized. Synchronized neural behavior reduces the number of possible states in which the brain can be. From the point of view of Shannon's Information Theory, synchronized behavior does not "add" but "reduces" the amount of information. Tononi believes that a better model for consciousness should focus on integrated information as obtained by the vast network of the brain (“Consciousness as integrated information”, 2008).
Global Neuronal Workspace
The "global neuronal workspace" model proposed by the French neuroscientist Stanislas Dehaene ("A Neuronal Model of a Global Workspace in Effortful Cognitive Tasks", 1998) blends Donald Hebb's cell assemblies, his mentor JeanPierre Changeux's (and Gerald Edelman's) neural Darwinism, Bernard Baars' global workspace and Antonio Damasio's convergence zones. Dehaene thinks that consciousness is due to the action of giant neurons whose axons spread throughout the brain, especially the ones in the pre-frontal cortex, as described by the Swiss neuroscientist Stephanie Clarke ("Direct Interhemispheric Visual Input to Human Speech Areas", 1997) and by the Australian neuroscientist Guy Elston ("The Pyramidal Cell in Cognition", 2001). These giant neurons spread information to many regions of the brain, and, when enough of these regions agree that some information is important, they synchronize into a state of "global communication". The main difference with Bernard Baars' "global workspace" is that Dehaene's "global neuronal workspace" is a hierarchy of neural networks (as explained in his original manifesto written with Changeux, "Hierarchical Neuronal Modeling of Cognitive Functions", 1998). In 2005 Dehaene and Claire Sergent pinpointed the P3 wave, corresponding to massive positive voltage ("Timing of the Brain Events Underlying Access to Consciousness during the Attentional Blink", 2005), as a signature of consciousness. The P3 wave, first described by the US psychologist Samuel Sutton ("Evoked Potentials Correlates of Stimulus Uncertainty", 1965), is the manifestation of several regions of the brain firing in a synchronized manner, i.e. (according to Pascal Fries' theory) of a vast network of information transmission. Dehaene believes that during conscious experience groups of neurons begin to fire in synchrony and then the synchronized firing extends throughout the cortex. That escalation causes the spike in voltage that is recorded as a P3 wave. There's a tipping point of neuronal activity beyond which a state of global synchronized activity quickly settles in. This point is equivalent to the "phase transition" in physics and to the "bifurcation" in mathematics. Conscious awareness of a stimulus happens about a third of a second after the stimulus has been received, the time that it takes for that "global ignition" to reach a stable state. The 40 Hertz wave that Crick and Koch popularized is not enough because Dehaene discovered that some unconscious states also produce it. Consciousness arises from an "amplification" of this activity. The synchronized firing at 40 Hz (and, more generally, of the gamma band) is necessary but not sufficient: it also takes the sudden surge (the P3 wave) for the brain to yield a conscious event. You can potentially think an infinite number of thoughts. Each of these potential thoughts must already be coded in your brain, even those that you will never think. This is made possible by a process of integration that pulls together "information" stored in both neighboring and very distant neurons, and integrated in higher cortical regions similar to Antonio Damasio's "convergence zones" with feedback going back to the lower regions in a manner similar to Gerald Edelman's "reentry". It is not enough for consciousness that information be interconnected in the higher regions of the cortex: this interconnection must also ignite a loop leading to a global workspace. Furthermore, the giant neurons that organize our conscious life are active all the time. We "think" all the time, even when we are not aware of it. The brain is a Darwinian machine, constantly producing "thoughts" that are then selected by the stimuli. Our brain generates thoughts all the time. This random "noise" helps increase the Darwinian variation and the chances that we will have the best possible thought for the next situation that we have to understand. Dehaene's model is similar to the model that Giulio Tononi and Gerald Edelman proposed in the same year ("Consciousness and Complexity", 1998). Your cortex has 16 billion neurons and they can be combined in many different ways to yield trillions of potential thoughts. The integration is what turns neural events into consciousness (echoing Giulio Tononi's motto of "Consciousness as Integrated Information", 2008). We are not conscious of most of what our brain does, of most of what our organs perceive and process. The unconscious performs "brute processing" of multiple parallel sensory inputs. Consciousness selects one of these preprocessed pre-thoughts and runs with it. He compares consciousness to the spokesperson of a large organization, where thousands of people are processing huge amounts of data, but the spokesperson gives one simple linear version of what is going on. Consciousness removes all the ambiguities, uncertainties and contradictions from the input data and creates a simple coherent truth. Dehaene's model admits five types of unconscious, not just one: the preconscious (the enormous number of thoughts that are randomly generated and ready to become conscious), the subliminal (processed stimuli that cannot generate the P3 wave of conscious thoughts and therefore can never become conscious), the disconnected (brain processes that are simply not connected with the cortex in a way that would give them a chance to become conscious, e.g. breathing and heartbeat), the diluted (the multitude of firing patterns that react to stimuli but need to be processed in working space in order to yield conscious thoughts), and the dormant memories that can become conscious again at any time.
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