Online research in philosophy

Merker's core idea, that the experience of being conscious reflects the interactions of actions, targets, and motivations in the upper brainstem, with cortex providing the content of the conscious experience, merits serious consideration. However, we have two areas of concern: first, that his definition of consciousness is so broad that it is difficult to find any organisms with a brain that could be non-conscious; second, that the focus on one cortical–subcortical system neglects other systems (e.g., basal forebrain and brainstem cholinergic systems and their cortical and thalamic target areas) which may be of at least equal significance. (Published Online May 1 2007).

I have suggested that the prefrontal cortex constitutes an ?executive committee? with five streams coming from posterior cortex and subcortical areas to five pre-frontal executive regions, each of which chairs at least one on-going ?sub-committee? and vies with the other executives for taking over central control of conscious attention and willed action. It is through the dynamic interaction of this executive committee that unified conscious experiences and a sense of continuous self-identity are created. There is growing evidence that the amygdala-orbitofrontal brain circuit, in particular, is crucial to impulse control, ?knowledge of good and evil,? personality, personhood, and even ?how X-me made Y-me do something.? There are striking examples of the ways that orbitofrontal and anterior cingulate ?committee members? can stage an insurrection against the dorsolateral prefrontal cortex executive chair.

A review of the patterns of brain activation observed in implicit and explicit memory tasks indicates that during conscious retrieval studied items are first retrieved nonconsciously and are retained in a buffer at the extrastriate cortex. It also indicates that the awareness of the retrieved item is made possible by the activation of a reentrant signaling loop between the extrastriate and left prefrontal cortices.

Awareness is a personal experience, which is only accessible to the rest of world through interpretation. We set out to identify a neural correlate of visual awareness, using brief subliminal and supraliminal verbal stimuli while measuring cerebral blood flow distribution with H215O PET. Awareness of visual verbal stimuli differentially activated medial parietal association cortex (precuneus), which is a polymodal sensory cortex, and dorsolateral prefrontal cortex, which is thought to be primarily executive. Our results suggest participation of these higher order perceptual and executive cortical structures in visual verbal awareness.