Interactions between neurons in the visual and frontal cortex during perception and awareness

Most theories hold that early visual cortex is responsible for the local analysis of simple features while cognitive processes take place in higher areas of the parietal and frontal cortex. However, these theories are not undisputed because there are findings that implicate early visual cortex in visual cognition - in tasks where subjects reason about what they see. Are these cognitive effects in early visual cortex an epiphenomenon or are they functionally relevant for these mental operations? I will discuss new evidence supporting the hypothesis that the modulation of activity in early visual areas has a causal role in cognition. The modulatory influences allow the early visual cortex to act as a multiscale cognitive blackboard for read and write operations by higher visual areas, which can thereby efficiently exchange information. I will next address how a conscious experience can emerge. Along the cortical hierarchy, a progressively larger proportion of cells modulate their spiking activity according to the subject's perceptual state, and the global workspace theory holds that stimuli only reach awareness as soon as they induce a special, "ignited" state in frontal cortex. We compared activity propagation from lower to higher cortical areas between perceived and identical non-perceived stimuli in V1, V4 and the dorsolateral prefrontal cortex of macaque monkeys. The animals carried out a task in which they reported the presence of a low-contrast stimulus with an eye movement. We found that low contrast stimuli that reached awareness elicited a stronger initial feedforward response at all these levels of the cortical hierarchy than stimuli that remained subliminal. Stimuli that reached awareness elicited a characteristic, "ignited" state. We could predict whether a weak stimulus reaches awareness based on the pre-stimulus brain state. Our findings provide new insights into the conditions that permit stimuli to enter into consciousness.