A theory of blindsight--the anatomy of the unconscious: a proposal for the koniocellular projections and intralaminar thalamus.

This paper extends the concepts introduced by the theory of premotor relations to unconscious cognitive mechanisms. According to the theory conscious mechanisms are associated with behavioural diversity, whereas unconscious output is proposed to have an obligatory association with stereotypical behaviour. The respective processes are by definition a function of the type of reafferent motor input. Concepts of simple and complex premotor networks are introduced as a means of describing unconscious and conscious processes, respectively. Evidence shows that unconscious cognitive performance differs qualitatively from conscious mechanisms suggesting parallel processes. Although the postulated anatomical substrates for conscious and unconscious processes will function in this model as parallel segregated networks, it is proposed they are distributed throughout the same cortical areas of the brain. Motor reafference is postulated to be mediated via pallidal projections to the thalamic reticular nucleus, which is known to modulate thalamocortical pathways. The role of the koniocellular pathway of the lateral geniculate nucleus remains an enigma and has some properties in common with the well-described magnocellular and parvocellular projections. There is also much speculation about the intralaminar and midline nuclei, the so-called non-specific thalamus. The paper will examine the distinctive features of thalamocortical networks and the role of the koniocellular pathway and intralaminar nuclei (ILN) of the thalamus and suggest that they form a neuroanatomical substrate for the categorizing of unconscious cognitive processes. The ILN has unique projections back to the basal ganglia, which could serve in constraining associated neocortical networks with stereotypical behaviour and thus putative unconscious processing. Only after establishing such a theoretical framework can one hope to successfully analyze the empirical literature on the syndrome of blindsight, of which a detailed account is presented. Blindsight refers to the apparent visual abilities of patients with damage to the striate visual cortex (VI). Patients will 'guess' the shape of an object or reach towards it when presented in the blind field, in spite of denying actually seeing it, i.e., they are unconsciously aware of it. Unlike the magnocellular and parvocellular geniculate pathways the koniocellular extrastriate projections partially conserve retinal information in these patients. Could the proposed network represent an anatomical model of the Freudian subconscious?