Objective: To assess the contribution of different anatomical brain sites to the genesis of P3 phenomena with respect to button pressing versus mental counting tasks.
Methods: Eight intractable epileptic patients undergoing depth electrode recordings prior to their surgery participated in the study. A total of 546 cerebral sites were recorded. A standard somatosensory oddball paradigm was used. The experiment was carried out in two sessions, differing in the requested responses to targets. The averaged responses in both tasks were compared.
Results: After targets, two kinds of P3-like potentials were observed within different cortical sites. Task-non-specific P3 potentials were seen for both types of responses to targets. The mean amplitude of these task-non-specific P3 potentials was significantly higher in the button pressing task. The intracerebral generators of this somatosensory P3 did not differ from the known generators of auditory and visual P3s. Task-specific P3-like potentials were found much less frequently. Button pressing unequivocally generated additional P3-like potentials in the premotor cortical sites. Mental counting repeatedly evoked additional P3-like waveforms in the left-side middle and inferior temporal gyri.
Conclusions: In addition to multiple intracerebral P3 generators that reflect target detection processing, other task-specific P3-like potential generators can be found in the human brain. Their activity may affect the topography and precise parameters of scalp P3 potential.