Functional Localization of Visual Motion Area FST in Humans

The fundus of the superior temporal sulcus (FST) in macaque monkeys is implicated in the processing of complex motion signals, yet a human homolog remains elusive. To better understand the neural mechanisms underlying the analysis of complex motion signals in humans, it is crucial to understand if and where a region homologous to FST exists. Here, we considered potential localizers and evaluated their effectiveness in delineating putative FST (pFST) from two nearby motion-sensitive areas, hMT and MST, in humans. Nine participants underwent fMRI scanning sessions with 2D and 3D motion localizers, as well as population receptive field (pRF) mapping. We observed consistent anterior and inferior activation relative to hMT and MST in response to stimuli that contained coherent 3D, but not 2D, motion. Motion opponency and myelination measures further validated the functional and structural distinction between pFST and hMT/MST. At the same time, standard pRF mapping techniques that reveal the visual field organization of hMT/MST proved suboptimal for delineating pFST. Our findings provide confirmatory evidence for the existence of a functional homolog of macaque area FST in humans, offer a robust framework for localizing pFST, and underscore the area's distinct role in visual motion processing.