Area 2 of primary somatosensory cortex encodes kinematics of the whole arm

Proprioception, or the sense of body position, movement, and associated forces, remains poorly understood, despite its clear importance to making coordinated movements. In the classic model of neurons in area 2, a proprioceptive area of primary somatosensory cortex, neural activity is related simply to the movement of the hand and interaction forces it encounters during movement, similar to our conscious experience of proprioception. However, in two separate experiments, examining 1) active and passive movements and 2) reaches to targets in two different workspaces, we found that a model of area 2 activity built on kinematics of the whole arm successfully predicted how features of neural activity changed across movement conditions, while the classic hand-based model was unable to. This suggests that, unlike our conscious experience and the classic model of proprioception in cortex, neural activity in area 2 represents movement of the whole arm.