Stimulus representations in body-selective regions of the macaque cortex assessed with event-related fMRI

Abstract

Functional imaging studies in humans and monkeys have shown category-selective regions in the temporal cortex, in particular for faces and bodies. Although the body-selective regions have been well studied in humans, little is understood about the functional properties of such regions in macaques. To address this, we first mapped body-selective activations in the visual cortex of four rhesus monkeys in a block design fMRI study and identified two regions in the middle and anterior Superior Temporal Sulcus (STS) that were more strongly activated by monkey bodies compared to well-controlled manmade objects. These two regions partially overlapped with regions that were more activated by faces than manmade objects. Secondly, using an event-related, single image fMRI design we measured the activations to 200 images of 10 stimulus classes (monkey bodies, human bodies, mammals, birds, monkey faces, human faces, body-like sculptures, fruits/vegetables, and two sets of control objects). Multivoxel-pattern analyses showed that both body-selective regions primarily distinguished faces from other inanimate and animate objects, including bodies. Another distinction was present between inanimate objects and bodies in the middle STS body region. The category-based clustering was less pronounced in the anterior compared to the middle STS body-selective regions. In addition, both body-selective regions showed further selectivity for different "subclasses" of the broad body category such as monkeys, human, mammals and birds. Overall, these data indicate strong spatial clustering of animate categories in the macaque STS with a surprisingly marked distinction between faces and bodies within body-selective regions which was stronger than between manmade objects and bodies.