Endogenous event-related potentials from sphenoidal electrodes.

Event-related potentials (ERPs) were recorded from left and right sphenoidal electrodes during 2 cognitive tasks (visual oddball and a word repetition procedure) known to evoke endogenous ERP activity in the medial temporal lobe. Both tasks gave rise to large, reliable modulations of scalp-recorded ERPs. In the oddball task, no consistent task-related ERP activity could be recorded from the sphenoidal electrodes concurrently with the scalp-recorded P3 component, although in the latency region following the peak of P3 these electrodes exhibited an enhanced late negative wave to target stimuli. In the word repetition task, no consistent repetition-related ERP effects of any kind were observed from the sphenoidal electrodes. Sphenoidal electrodes do not appear to detect the endogenous ERP components that are generated in the medial temporal lobe concurrently with scalp-recorded components.