I have been looking at a paper that is not very recent but none the less very interesting. It took ages to find a copy of it that I could access and download but now when I go back it is no longer there. The paper is E. Roy John; The neurophysics of consciousness; Brain Research Reviews, 39, 2002 pp 1-28. Those of you who have access to various sources will be able to download the pdf but I can no longer supply a link.
The paper describes a proposed global brain process. There are local processes to establish ‘fragments of sensation’ and these are connected to give ‘fragments of perception’, but a complete ‘frame’ of perception requires non-local processing. Consciousness appears to require a brain-wide process. John sees these processes in terms of EEG patterns. I am going to deal with his theory in several posts rather than try to put everything in one. In this post is John’s diagram of consciousness and descriptions of the numbered phases. I feel there are some ‘almighty leaps’ here but there are also some very convincing processes too.
Perceptual frame opens:
process 1 – stimuli from the environment are captured by the sense organs and directed to the thalamus
process 2 – input in the thalamus is directed to the thalamic regions specific for each modality/sense
process 3 – the thalamic regions send volleys, by fast, direct paths to the cortical primary sensory areas of the cortex, the volleys are parsed into perceptual frames – the information is distributed in the sensory cortex and decomposed into ‘fragments of sensation’
process 4 – activity in the local ensembles becomes non-random, and local negative entropy deepens
process 5 - each perceptual frame lasts ~70–100 ms (1 / alpha frequency) and successive frames are each offset by 20–25 ms (1 / gamma frequency) - “this multiplexed activity will produce a steady state which will persist independent of the discharge of particular neurons” (sample and hold).
Now we have a perceptual frame – a field potential pattern throughout the cortex controlled by volleys of sensory specific thalamo-cortical signals.
Relevant context is represented:
At the same time as the processes above, 1 to 5, other information is entering the frame.
process 6 – activity in the thalamus also activates other (non-cortical) regions such as the brainstem, cerebellum, and limbic system which are primed by inputs in the immediate past
process 7 – this activity adds information from recent working memory, episodic memories, states of autonomic, emotional, motivational and motor systems to the non-sensory thalamic regions where this information forms a value/meaning and is directed to cortical areas by the thalamus – it arrives after the original sensory data because of its longer path and provides context to the ‘sample and hold’.
Sensory fragments are converted to fragments of perception:
process 8 – as frames coalesce, elements with most relevance (strong value signal) deliver stronger signals to the comparator system distributed throughout the cortex
process 9 – those pyamidal cells whose fields produce ‘fragments of sensation’ and who also have value signal input, shift their membrane potential above a critical threshold, giving a higher rate of cortico-thalamic activity. This selects them automatically to convert to ‘fragments of perception’.
Perceptual elements are bound together:
“A cooperative process is required for the multidimensional binding which provides the fine texture of consciousness and the global nature of a momentary cognitive instant of experience. No cell nor ensemble can subserve the large scale integration required for cognitive interpretation of the totality of significant departures from randomness which constitutes the GNEGP (global negative potential), the integration of LNEGP (local negative potential) activity synchronized across spatially distributed neuronal masses. The actual binding process has been envisaged as a global resonance state, resulting from the coincidence detection of concurrent specific and nonspecific neuronal processes.”
process 10 - rhythmic oscillatory potentials, synchronous and phase-locked across the cortex, act like a scanning voltage which modulates the membrane potentials of the cortical cells. “Rhythmic fluctuation of cortical membrane potentials intensifies a multi-modal cortico-thalamic volley of the distributed LNEGP fragments of perception that is synchronously projected from many cortical areas upon appropriate thalamic regions. These fragments of percepts converge as a coherent cortico-thalamic volley upon the intralaminar nuclei of the thalamus, where they are ‘bound’ into the multimodal, global negative entropy of perception, GNEG- P1. GNegP is the information content of momentary self-awareness.”
process 11 - At the same time signals cause the nucleus reticularis of the thalamus to inhibit the thalamic regions from sending signals to areas of the cortex that have not been caught up in the concordance that produced the GNEGP. This defines the information content of the moment of awareness.
Consciousness emerges from resonating organized energy:
“A reverberatory thalamo-cortico-thalamo interaction arises between the thalamic nodes representing GNEGP and those brain regions wherein LNEGP arose, which endows GNEGP1 with specific sensory and emotional dimensions, the ‘qualia’ of the subjective experience.”
process 12 – At the same time, the global perception is projected from the thalamus to the consciousness system, the set of brain regions which change state reversibly with loss of consciousness, causing the consciousness system to becomes highly coherent.
Process 13 - “coherent activation within this set of structures transposes GNEGP into a concentrated electromagnetic field. Establishment of a sufficiently non-random spatio-temporal charge aggregate within a critical neural mass is postulated to produce consciousness, an emergent property of sufficiently organized energy in matter.” This coherent reverberating activation in the CS acts like an ‘analog’ electrical field in a restricted space. John says that the brain is a hybrid digital-analog system.
The content of consciousness and the self:
process 14 - resonance between the consciousness system and the intralaminar nuclei of the thalamus, the percept is given the qualia of the primary sensory regions of the cortex.
process 15 - subjective awareness emerges as an intrinsic property of the coupling of the analog CS with the digital microstate. “It is postulated that much of the early life of human beings is devoted to learning how to reconcile these two classes of brain activity”
process 16 - “the resonant activity impinging upon the adaptive output systems provides feedback to update the value system. Interactions of the intralaminar nucleus and other thalamic nuclei with CS structures modulate efferent systems to produce adaptive outputs such as speech, movement and emotional expression”
More in future posts.