Simultaneous recordings from posterior and anterior body-responsive regions in the macaque Superior Temporal Sulcus.

Abstract

Using fMRI we mapped body patches in the macaque temporal visual cortex with videos of acting monkeys contrasted to dynamic monkey faces and objects. These patches are located in the upper bank/ fundus and lower bank of the Superior Temporal Sulcus (STS) and ventral to the STS. The anatomical organization of body-responsive regions can reflect functional differences, namely a difference in motion sensitivity along the dorso-ventral axis (VSS, Raman et al., 2023) and a difference in the complexity of feature coding along the visual hierarchy. To address the static feature selectivity of single neurons and recurrent interaction between these patches, we created a stimulus set of 720 stimuli, in which the same monkey avatar had 45 different body postures, rendered from a horizontal and top view from 8 different viewing angles. We targeted simultaneously both the fMRI-defined mid-STS (MSB) and anterior-STS body patch (ASB) using 16 channel V-probes. To identify body-responsive channels, multiunit data was collected from a test using the same videos of bodies, faces and objects as in the fMRI mapping study. Thereafter the 720 static stimuli were presented for 200 ms during passive fixation. Analyzing the simultaneously recorded units from MSB and ASB, we found that the average response onset of the MSB neurons preceded around 20 ms those of ASB. Both patches showed a decrease in response after the initial response transient followed by a second response. This second response phase showed the same latency difference between patches as the initial response onset. Thus, by using these well-visible, unoccluded stimuli, we did not find evidence for a top-down modulation of MSB response by ASB. Instead, the second response phase appears to result either from bottom-up or within-patch recurrent activity.