Intracranial Electrical Stimulation of the Superior Temporal Gyrus Evokes Rapid Responses in Human Visual Cortex.

Sounds can alter visual processing even at the earliest stages of the cortical pathway. However, our understanding of how acoustic signals are relayed to visual cortex is limited, particularly with respect to the involvement of different regions of auditory cortex in the most rapid stages of this communication across distinct visual areas. Here, we address this question by examining occipital intracranial responses to direct electrical stimulation of the superior temporal gyrus (STG) in 23 patients with epilepsy. Stimulation of mid- and posterior-STG elicited responses in visual cortex as early as 18 ms after onset, with a distribution that favored lateral occipital cortex, lingual gyrus, and anterior calcarine regions near peripheral V1. Early visual cortex (V1/V2) responded most strongly to stimulation over mid-STG, whereas lateral occipital cortex (near V5/hMT+) exhibited the most robust response to posterior STG stimulation. Responses in visual cortex were organized in a manner similar to that of nonhuman primates, with possible evidence for an exception over the occipital pole. These results support theories that human visual responses to sound are inherited in part from auditory cortex and provide insight into routes through which acoustic information may rapidly facilitate processing of visual input.