Somatosensory input to auditory association cortex in the macaque monkey

We investigated the convergence of somatosensory and auditory inputs in wit hin subregions of macaque auditory cortex. Laminar current source density a nd multiunit activity profiles were sampled with linear array multielectrod es during penetrations of the posterior superior temporal plane in three ma caque monkeys. At each recording site, auditory responses to binaural click s, pure tones, and band-passed noise, all presented by earphones, were comp ared with somatosensory responses evoked by contralateral median nerve stim ulation. Subjects were awake but were not required to discriminate the stim uli. Borders between A1 and surrounding belt regions were identified by map ping best frequency and stimulus preferences and by subsequent histological analysis. Regions immediately caudomedial to A1 had robust somatosensory r esponses corepresented with auditory responses. In these regions, both soma tosensory and auditory response profiles had "feedforward" patterns; initia l excitation beginning in Lamina 4 and spreading to extragranular laminae. Auditory and somatosensory responses displayed a high degree of temporal ov erlap. Anatomical reconstruction indicated that the somatosensory input reg ion includes, but may not be restricted to, the caudomedial auditory associ ation cortex. As was earlier reported for this region, auditory frequency t uning curves were broad and band-passed noise responses were larger than pu re tone responses. No somatosensory responses were observed in A1. These fi ndings suggest a potential neural substrate for multisensory integration at an early stage of auditory cortical processing.