The P300 event-related potential. I. Theoretical and psychobiological perspectives.

The P300 is a positive wave which arises when an attended stimulus is detec ted. Its parameters depend on a number of variables, in particular the subj ect's mental state, the task that has to be accomplished, the significance of the stimulus, and the degree of attention. It can be recorded with accur acy, and the different stages of information processing can therefore be an alyzed. The P300 wave shows the modifications in neuronal activity wh ich t ake place during the cognitive process: P300 latency provides an indirect i ndication of the duration of the processes involved in stimulus discriminat ion while its amplitude, which is influenced by a number of variables, prov ides an index of the intensity of the energetic activation or arousal invol ved. The P300 wave consists of several components which reflect distinct in formation-processing events (P3a, P3b, P3e, P-SR, P-GR). According to the t heoretical models, it is hypothesized that P300 could either represent the adaptation of the working memory to further environmental input ('context u pdating'), or indicate a closing process ('context closure') in information processing. As regards the physiological aspect of P300 and its associatio n with cortical networks, various studies have suggested that several corti cal generators of P300 may co-exist: the medial temporal lobe, the temporo- parietal junction, and the medial and lateral frontal lobe. Psychopharmacol ogical studies have shown that different neurotransmitter systems are invol ved in the generation and modulation of P300, namely the cholinergic, norad renergic, dopaminergic, serotoninergic and gabaergic systems. It appears th at the noradrenergic agonists increase the amplitude of P300, dopaminergic agonists may have a biphasic effect (increase/reduction), while cholinergic antagonists and gabaergic agonists reduce P300 amplitude and prolong its l atency. (C) 2000 Editions scientifiques et medicales Elsevier SAS.