Excitation at widely dispersed loci in the cerebral cortex may represent a neural correlate of consciousness. Accordingly, each unique combination of excited neurons would determine the content of a conscious moment. This conceptualization would be strengthened if we could identify what orchestrates the various combinations of excited neurons. In the present paper, cholinergic afferents to the cerebral cortex are hypothesized to enhance activity at specific cortical circuits and determine the content of a conscious moment by activating certain combinations of postsynaptic (...) sites in select cortical modules. It is proposed that these selections are enabled by learning-related restructuring that simultaneously adjusts the cytoskeletal matrix at specific constellations of postsynaptic sites giving all a similar geometry. The underlying mechanism of conscious awareness hypothetically involves cholinergic mediation of linkages between microtubules and microtubule-associated protein-2 . The first reason for proposing this mechanism is that previous studies indicate cognitive-related changes in MAP-2 occur in cholinoceptive cells within discrete cortical modules. These cortical modules are found throughout the cerebral cortex, measure 1–2 mm2, and contain approximately 103–104cholinoceptive cells that are enriched with MAP-2. The subsectors of the hippocampus may function similarly to cortical modules. The second reason for proposing the current mechanism is that the MAP-2 rich cells throughout the cerebral cortex correspond almost exactly with the cortical cells containing muscarinic receptors. Many of these cholinoceptive, MAP-2 rich cells are large pyramidal cell types, but some are also small pyramidal cells and nonpyramidal types. The third reason for proposing the current mechanism is that cholinergic afferents are module-specific; cholinergic axons terminate wholly within individual cortical modules. The cholinergic afferents may be unique in this regard. Finally, the tapering apical dendrites of pyramidal cells are proposed as primary sites for cholinergic mediation of linkages between MAP-2 and microtubules because especially high amounts of MAP-2 are found here. Also, the possibility is raised that muscarinic actions on MAP-2 could modulate microtubular coherence and self-collapse, phenomena that have been suggested to underlie consciousness. (shrink)

I dispute that consciousness is generated by core circuitry in the forebrain, with predominance of motor areas, as Cotterillproposes in Enchanted Looms and other theorists do also. Ipropose instead that conscious contents are the momentary modeof action of the integrated cortical field, expressed as a point vector ( dominant focus ), to which, in varying degree, allsectors of the network contribute. Consciousness is the brain''saccess to its own activity space, and is identical with the moment''sdominant mode of activity. The dominant (...) focus is generally weightedtoward enactively encoded percepts. Anticipation and preparation,perception and action, inextricably interdigitate. I also dispute the view of Cotterill and others that consciousnesshas unique agency, which bestowed adaptive advantage when the brain evolved. Being identical with the activity of the network,consciousness can have no additional agency, and it can offerno adaptive advantages beyond those that characterize the network. (shrink)