Biological motion processing in the macaque-fMRI

Abstract

Psychophysical and imaging studies in humans have demonstrated specialized mechanisms for the detection of biological motion. Studies in humans, however, are limited in the details of these mechanisms they can reveal. We used functional MRI in the anaesthetized macaque to identify the brain areas involved in the analysis of biological motion and thereby provide electrode-guidance to study these mechanisms in more detail. We used a human point-light walker and a scrambled walker. The latter has identical local motion signals to the intact walker, but its local signals do not combine to a figure of a walking human. In a block-design we alternated these stimuli with periods of no visual stimulation. We recorded the BOLD response in a 4.7T vertical scanner (Bruker, Inc) using gradient-recalled multi-shot multi-slice EPI sequences. 21 horizontal slices covered the whole brain. Voxels were 1x1x2mm, TE =20ms, TR=1058ms. The data were analysed in BrainVoyager (BrainInnovation, Inc). Both the intact walker and the scrambled walker significantly activated early visual areas V1, V2 and the motion areas V3 and MT. More interestingly, we also found activation of areas commonly associated with form analysis such as V4 and the mid-anterior STS. Apparently, these areas are equipped with the neural mechanisms to detect the typical pendular movement associated with biological motion. In our setup, however, the intact walker never activated these areas significantly more than the scrambled walker