Auditory cortex on the human posterior superior temporal gyrus

The human superior temporal cortex plays a critical role in hearing, speech, and language, yet its functional organization is poorly understood. Evoked potentials (EPs) to auditory click-train stimulation presented binaurally were recorded chronically from penetrating electrodes implanted in Heschl's gyrus (HG), from pial-surface electrodes placed on the lateral superior temporal gyrus (STG), or from both simultaneously, in awake humans undergoing surgery for medically intractable epilepsy. The distribution of averaged EPs was restricted to a relatively small area on the lateral surface of the posterior STG. In several cases, there were multiple foci of high amplitude EPs lying along this acoustically active portion of STG. EPs recorded simultaneously from HG and STG differed in their sensitivities to general anesthesia and to changes in rate of stimulus presentation. Results indicate that the acoustically active region on the STG is a separate auditory area, functionally distinct from the HG auditory field(s). We refer to this acoustically sensitive area of the STG as the posterior lateral superior temporal area (PLST). Electrical stimulation of HG resulted in short-latency EPs in an area that overlaps PLST, indicating that PLST receives a corticocortical input, either directly or indirectly, from HG. These physiological findings are in accord with anatomic evidence in humans and in nonhuman primates that the superior temporal cortex contains multiple interconnected auditory areas.