Abstract representations of grasping action parameters in the dorsal stream

The dorsal visual stream supports reaching and grasping with one’s hands. However, it remains unclear how the dorsal stream supports comparable actions if the action is not performed manually. Specifically, here we tested if the dorsal stream encodes the size of an object involved in the action, regardless of what body part interacts with it. To address this, in the current fMRI study we examined activation during grasping performed by two different body parts – the right hand and the right foot, while varying the size of the grasped object. To determine whether there is a shared representation for grasping size for both foot and hand, we conducted a multivariate pattern analysis to decode patterns across effectors, and trained the classifier to decode size for the hand and tested on the foot and vice versa. The results indicate that decoding grasping size was possible across the hand and the foot, in the Inferior parietal lobe (IPL) within the dorsal visual stream, as well as in motor cortices such as M1 and the ventral premotor cortex (PMv). These findings suggest that the dorsal stream action representations are independent from specific motor parameters such as the body part performing the action.