Abstract
Neuroimaging studies have identified the posterior superior temporal sulcus (STSp) as the brain area active during perception of biological motion (i.e. Grossman & Blake, 2002; Beauchamp et al., 2002). The STSp has also been identified in tasks that require understanding of social interaction and animacy through interactive dynamics (Martin & Weisberg, 2003). The current study measures brain activity associated with these two types of tasks to determine whether the biological motion responses are associated with the same or a distinct brain area as social understanding. Method: The visual STSp was identified as the brain area that responds more during blocks of point-light animations of human actions as compared to blocks of motion-matched ‘scrambled’ animations (Grossman et. al, 2000). The social STSp was identified as the brain area more activated by simple geometric shapes interacting in a social manner (e.g. chasing, dancing, or playing) as compared to mechanical type animations (Martin & Weisberg, 2003). Results: As reported in the literature, both localizers identified regions on the STS. Within-subject analysis revealed these brain areas to be adjacent with distinct foci, with some partial, peripheral overlap in some subjects. In all cases the point-light localized STSp was more anterior than the social selective area. Functional patterns of neural activity in the visual STS area dissociated the social and mechanical animations, similar to the social region. The reverse was not true, however: neural activity in the social STS area did not discriminate between biological and scrambled animations. Conclusions: These results suggest that the cortical areas optimally driven by observing human actions are not the same as those driven by observation of social interaction. A more sophisticated understanding of STS cortical organization is required to parse out the complex patterns in this brain area.
We thank Alex Martin for the social interaction stimuli.