Motion- and shape-based body-selectivity in macaque anterior inferotemporal cortex

Abstract

Visual analysis of body movements is an essential element of non-verbal social communication. fMRI studies have identified body patches in the macaque inferotemporal (IT) cortex that were activated more strongly by static images of bodies compared to images of faces and objects. However, the organization of “dynamic” body patches that are activated by dynamic bodies, and their feature selectivity at the single-cell level are still unknown. In this fMRI-guided electrophysiological study, we investigated the neural representations underlying the visual processing of dynamic bodies in the dynamic body patches of the macaque’s brain. We first localized the dynamic body patches using a set of 1 s long videos of dynamic monkey bodies, dynamic monkey faces, and dynamic artificial objects. We found several dynamic body patches that were neighboring face patches along and ventral to the Superior Temporal Sulcus (STS). Then, we recorded body-selective single cells, identified with the same videos as for the fMRI mapping, in an anterior dynamic body patch, ventral to the STS in two monkeys. The majority of neurons responded only during a segment of the video and showed high selectivity for different body videos. Most neurons had a similar response profile for the original videos and a version in which the body was reduced to its silhouette. To assess the contribution of motion, we also measured the response to static frames ("snapshots”) of the videos. Many neurons responded equally well to the static presentations of snapshots and the original videos, while others responded only to the videos, requiring motion. The latter cells were also selective for the order of the frames of a video. These findings suggest that the majority of body-selective cells in anterior IT are shape-selective and some of these cells, located ventral to the STS, also encode the snapshot sequence.