The visual dorsal stream processes tool-use actions regardless of body part even in people born without hands

The visual dorsal stream subserves vision for action. Previous research has shown that much of the dorsal stream encodes information about actions, particularly hand actions. However, the extent to which this information is abstract, or independent of visual and motor properties, is unclear. A high-level of abstraction would predict a consistent representation of the same actions, even if performed using another body part (effector) with different visual and motor properties. Here, we leveraged functional neuroimaging in typically developed controls and individuals born without hands to understand the abstraction level of motor representation. fMRI data from control subjects (n=13) and people born without both hands (n=3) were collected while participants completed tool-use and grasping actions with their dominant right hand and/or foot. Analyses suggested that actions are indeed represented at a high level of abstraction in the left anterior intraparietal sulcus (aIPS), left premotor cortex (PMd), and left supplementary motor area (SMA). Specifically, univariate activation levels showed similar preferences for tool-use actions for both the hand and foot. Moreover, multivariate action patterns could discriminate between actions, even across effectors. Importantly, action preferences and decoding were found in people born without hands, suggesting motor hand imagery is an unlikely cause for these findings. This implies that some areas of the visuomotor system have abstract representations that extend beyond visual and motor parameters to represent higher-order goals of specific actions.