Proprioception and Body Schema

Close your eyes and touch your nose. You succeed because of proprioception — the sense of your body's position and movement in space. The term was coined by Charles Sherrington in The Integrative Action of the Nervous System (1906), and for most of the twentieth century proprioception was treated as a well-understood modality: muscle spindles and Golgi tendon organs send signals to the brain about joint angle and muscle length, and the brain assembles these into a coherent body map. But the map is stranger than it appeared. In 1998, Matthew Botvinick and Jonathan Cohen demonstrated the rubber hand illusion: when a visible rubber hand is stroked in synchrony with a person's hidden real hand, the brain rapidly incorporates the rubber hand into the body schema — and the person feels the touch on the rubber hand. V. S. Ramachandran's work on phantom limbs showed that the body schema persists even after the limb is gone, generating vivid and sometimes painful sensations in absent fingers and toes. Shaun Gallagher's distinction between body schema (unconscious, motor) and body image (conscious, perceptual) revealed that proprioception operates at multiple levels. Yet the fundamental question — how the brain constructs, maintains, and updates a real-time model of the body from noisy, delayed, and sometimes contradictory sensory signals — remains open. The Academy hosts Proprioception in the Body School because without it, no game is playable. It is the precondition of all embodied action, and we do not fully understand how it works.

Charles Sherrington, The Integrative Action of the Nervous System (Yale University Press, 1906). Matthew Botvinick and Jonathan Cohen, "Rubber Hands 'Feel' Touch That Eyes See," Nature 391(6669), 1998. V. S. Ramachandran and Sandra Blakeslee, Phantoms in the Brain (William Morrow, 1998). Shaun Gallagher, How the Body Shapes the Mind (Oxford University Press, 2005). Henrik Ehrsson, "The Experimental Induction of Out-of-Body Experiences," Science 317(5841), 2007. The multisensory integration framework surveyed in Matthew Longo et al., "What Is Embodiment?", Psychonomic Bulletin & Review 15(6), 2008.