PATTERN OF NEURONAL-ACTIVITY ASSOCIATED WITH CONSCIOUS AND UNCONSCIOUS PROCESSING OF VISUAL SIGNALS

Following striate cortex damage in monkeys and humans there can be res idual function mediated by parallel visual pathways, In humans this ca n sometimes bk associated with a ''feeling'' that something has happen ed, especially with rapid movement or abrupt onset, For less transient events, discriminative performance may still be well above chance eve n when the subject reports no conscious awareness of the stimulus, In a previous study we examined parameters that yield good residual visua l performance in the ''blind'' hemifield of a subject with unilateral damage to the primary visual cortex, With appropriate parameters we de monstrated good discriminative performance, both with and without cons cious awareness of a visual event, These observations raise the possib ility of imaging the brain activity generated in the ''aware'' and the ''unaware'' modes, with matched levels of discrimination performance, and hence of revealing patterns of brain activation associated with v isual awareness, The intact hemifield also allows a comparison with no rmal vision, Here we report the results of a functional magnetic reson ance imaging study on the same subject carried out under aware and una ware stimulus conditions, The results point to a shift in the pattern of activity from neocortex in the aware mode, to subcortical structure s in the unaware mode, In the aware mode prestriate and dorsolateral p refrontal cortices (area 46) are active, In the unaware mode the super ior colliculus is active, together with medial and orbital prefrontal cortical sites.