Body-selective single cell responses in the macaque middle superior temporal sulcus body patch defined by fMRI

Single-cell and fMRI studies in non-human primates have shown responses to faces and body parts in the inferotemporal cortex. Previously, we mapped body category selective patches in the cortex using fMRI in awake monkeys (Popivanov et al., SFN 2010). Now we recorded single cell spiking and local field potential (LFP) activity in and surrounding an fMRI defined body patch to determine the selectivity for animate and inanimate objects. The stimuli were identical to those used in the fMRI mapping and consisted of monochrome images of headless monkey and human bodies (various postures), two sets of man-made objects - matched for each of the body categories, monkey and human faces (various views), four-legged mammals, birds, fruits, and Moore sculptures. The monkey and human bodies were matched for area and aspect ratio to their corresponding objects. The areas of all other stimulus categories were matched to those of the monkey bodies. The luminance of all stimuli was equated. Each category included 10 images. All stimuli were embedded into a pink noise background, covering the whole display. A block design fMRI localiser was used to define the body-responsive patches (contrast between monkey bodies and their matched objects). We recorded in and around the middle superior temporal sulcus (STS) body patch (2-3 mm anterior to the auditory mediatus) which is one of two main body-responsive fMRI defined patches. Stimuli were shown for 200 ms during a fixation task. Stimulus position was adapted to the receptive field of the neuron. Single neurons in the body patch responded on average significantly more strongly to images of bodies (monkey, human, mammal and bird) than to the other stimulus categories, including faces. However, all single neurons showed a profound difference in response to the different body images, even within the monkey body category. Cluster analysis of the neural distances between the images based on net spiking responses showed two main clusters -all bodies (monkeys, humans, mammals, and birds) vs. all other stimuli (mainly faces, objects, fruits, and sculptures). This category selectivity for bodies at the population level was more pronounced for the high gamma LFP power. Lateral to the body patch at the same A/P level, neurons responded to bodies as well as to faces, but less to the other categories. Cluster analysis of spiking responses and especially the high gamma power showed distinct grouping of faces (monkey and human) vs. bodies vs. other inanimate stimuli. These data demonstrate that single neurons in the middle STS body patch respond on average stronger to bodies than to other categories but also show strong within-body category stimulus selectivity.status: publishe