On the Neurophysiology of Consciousness: I. An Overview

How certain neural mechanisms (Mc) momentarily endow with subjective awareness (C) percepts and affects represented elsewhere is more likely to be clarified when structures essential to Mc are identified. The loss of C with bilateral thalamic lesions involving the intralaminar nuclei (ILN) contrasts with retention of C after large cortical ablations depriving C of specific contents. A role of ILN in the perception of primitive (i.e., not cortically computed) sensations is suggested by their afference of directly ascending pathways. A role for ILN in awareness of cortical activity is suggested by their widespread afference from cortex, a property shared with striatum. A role for ILN in volition is suggested by their heavy projection to striatum. Unlike striatum, ILN also project widely to almost all neocortex, enabling an effect on ideation; this last property is in common with other structures (e.g., locus coeruleus) but none of them has the same direct cortical afference. And passage through the reticular nucleus (nRt) of ILN efferents to cortex could impact the attention-selective action of nRt. It is suggested that the quickest route to a better understanding of C involves more intensive study of ILN. No other structure seems, in the light of our current knowledge, a more likely site for Mc.