Source Imaging of P300 Visual Evoked Potentials and Cognitive Functions in Healthy Subjects.

The P300 event-related potential (EPR) is regarded as a neurophysiological indicator of cognitive processing of a stimulus. However, it is not known whether the P300 is a unitary component recorded on the scalp as a result of the activity of a specific intracerebral structure, or if it represents the sum of underlying components that may reflect the activation of broadly distributed intracerebral structures. The objective of the present experiment was to investigate possible correlations among the source(s) involved in the generation of the P300 and their possible neurocognitive function. The visual-evoked potential (VEP) was elicited by the oddball paradigm and analyzed after employment of sLORETA (standardized low-resolution electromagnetic tomography). The window of the P300 wave encompasses the period during which the response to the target and nontarget condition differs significantly (≈375 ms to ≈465 ms, with a peak at ≈422.5 ms). The results showed sequential and what appeared to be logical activation patterns of specific structures (specific for the processing of the stimulus used here) after presentation of the target stimulus. The peak of the P300 wave represented activation of the parahippocampal gyrus, which is responsible for upgrading memory in response to a target stimulus.