Depth electrode recordings show double dissociation between pitch processing in lateral Heschl’s gyrus and sound onset processing in medial Heschl’s gyrus

Abstract

Pitch is a fundamental perceptual attribute of sounds. Our ability to discriminate, separate, and identify sounds relies heavily on pitch. Recent neuroimaging studies in humans have provided converging evidence for the existence of a "pitch center"--a region on the superior temporal plane (STP) lateral to Heschl's gyrus specialized in pitch extraction--but a direct confirmation is still missing. Intracerebral recordings in humans are ideally suited for such a confirmation. Here we report results from depth electrode recordings in a patient undergoing investigation for epilepsy. We demonstrate a double dissociation between responses from the medial and lateral STP around Heschl's gyrus to the onset of sound energy and the onset of pitch. Three pieces of evidence support this finding: (1) the response to sounds that do not contain pitch is small in the lateral STP compared to the medial STP; (2) sounds that contain pitch evoke a strong response in the lateral STP; (3) at the transition from noise to a specialised noise-like, but tonal, sound referred to as iterated ripple noise, where the onset of pitch is the sole acoustic event, only the lateral contact showed a response. Our results provide direct evidence for a pitch-specific area on lateral STP with intracranial recordings from the human auditory cortex.