Electrical stimulation of the superior temporal gyrus evokes rapid responses in human visual cortex

Sounds elicit rapid responses in human visual cortex. Anatomical work in nonhuman primates suggests that these responses may be enabled by monosynaptic, corticocortical projections between auditory and visual areas. Such projections would not only provide routes for rapid modulation of visual processing in the sighted, but also avenues for cortical adaptation following vision loss. However, there is little available information on the presence and organization of such projections in humans. Here, we address this question by examining intracranial responses to direct electrical stimulation of the superior temporal gyrus (STG) in 23 patients (both male and female). Mid- and posterior-STG stimulation produced rapid responses in early visual cortex (18ms+), with a distribution that favored lateral occipital cortex 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. These data demonstrate that communication from auditory to visual cortex can occur in humans at latencies that are compatible with corticocortical, potentially monosynaptic, transmission. Responses in visual cortex were organized in a manner similar to that of nonhuman primates, with preliminary evidence for an exception over the occipital pole. Overall, the results provide support for theories that human visual responses to sound are inherited, in part, from auditory cortex.