Distinct patterns of whole-body coding in human motor cortex and posterior parietal cortex

Traditional views of cortical motor areas hold that movements of different parts of the body, or effectors, are represented in distinct anatomical locations. The extent of overlap in effector representations has been a topic of debate for decades. We recorded from single neurons in 'hand areas' of motor cortex (MC) and posterior parietal cortex (PPC) of tetraplegic humans while they attempted movements across the body. We found a population response to every movement tested in both areas; however, the hand knob of MC more selectively activated for hand movements, whereas PPC did not emphasize any specific effector. Single neurons in MC responded selectively to a single effector or to two effectors that were part of the same limb. In PPC, neurons responded to random combinations of effectors. These findings suggest a transition from highly effector-general representation in PPC to regional effector specificity in MC.