The localization of brain generators of cognitive potentials can provide insight into the composition and function of neuronal networks underlying various cognitive functions. An indirect indication of the importance of brain regions on scalp recorded P300 can be provided by the recordings in patients with circumscribed brain lesions. The activity of the temporo-parietal junction, and in some cases also the activity of the hippocampus, the dorsolateral prefrontal cortex, and the thalamus, and possibly even of some other regions, modulates the activity that provides the basis for the scalp recorded potentials. The source locations can be directly studied using intracerebral recording. In the human brain, a widespread distribution of P3-like potential generators in multiple cortical and subcortical regions has been observed. The participation of widespread areas of the frontal, temporal and parietal cortex, in addition to the cingulate and mesial temporal regions and the basal ganglia and thalamus, has been shown. Intracerebrally, in addition to the multiple task-nonspecific P3 generators, other task-specific P3-like potential generators have been recorded. A variable and task-dependent internal organization of cortico-subcortical systems generating the P300 is probable.
The source of scalp-recorded P300 remains a subject of ongoing discussion. The contribution of individual cortical areas generating P3 potentials remains unclear. We strongly suspect that scalp-recorded P300 represents a summation of potentials that are generated simultaneously in several cortical as well as in several subcortical structures.