Chapter 45 P300 and conscious perception

Abstract

This chapter discusses the neurophysiological approach of simple conscious mechanisms and instrument precise designs for assessing in detail the specific interventions of the brain conscious mechanisms during each fraction of a second of active behavior. An essential asset of brain electrophysiology research is accuracy in time to identify sequential interacting processes and their topographies (brain mapping). Studies of nonaveraged brain responses provide unmatched instruments for realistically assessing brain versatility during sensory inputs processing and adaptive perceptual decisions. Simple conscious decisions about target sensory stimuli can be studied physiologically and brain mapping methods, using nonaveraged single responses, have disclosed important new data, emphasizing the split-second versatility of human brain operations. The P300 electrogenesis exerts an inhibitory and/or disfacilitatory action over the cortical neuronal assemblies, subserving the parieto-prefrontal 40Hz phase-lock and conscious perceptual decision, thereby completing the cognitive processing of the attended target input when the latter has been identified. The P300 electrogenesis is known to occur in conjunction with selective attention to a “target” event for which the subject is searching among a series of sensory inputs. Current scalp recording studies of P300 make ample use of Go–NoGo experimental series, in which the subject is required to respond to each rare sensory stimulus, and refrain from responding to the randomly intermixed frequent stimuli. There is current agreement that P300 is widespread over the scalp and in certain subcortical structures and that it is not an early cognitive activity of the brain. A case can be made for P300, not being involved in the brain processes, identifying the target input. The main reason is that P300 occurs too late, that is after the motor decision, to press the key already been made. The time histogram of key presses to the average target stimuli shows a wide time overlap with the concomitant P300.