The brain's orienting response (novelty P3) in patients with unilateral temporal lobe resections

► The cortical sign of the orienting response, the P3a, habituates to novel repetition. ► The hippocampus contributes to this scalp-recorded potential. ► We studied P3a habituation in patients with unilateral removal of the entire hippocampus. ► Normal controls, but not patients, showed reliable P3a habituation. ► We conclude that bilaterally intact hippocampi are critical to show P3a habituation.