Monkey primary somatosensory cortex has a proprioceptive representation of eye position

The visual system is tied to the retina. Because the eyes move in the orbit, and the head moves on the body, accurate location of an object in extrapersonal space cannot simply result from a visual signal. Instead, the retinal signal must be combined with an estimate of where the eyes are in the orbit, and where the head is in space, to calculate where that object is relative to the observer. There is abundant evidence for eye position signals in various areas of the visual cortex. However, the source of that eye position signal is unknown. Estimates of eye position can arise from two different sources. One is outflow, an 'efference copy' or 'corollary discharge' which might arise from some eye position signal used to specify eye position for the eye muscles. The second source is inflow, a direct proprioceptive signal from the muscles themselves. Nevertheless, neither a proprioceptive representation of eye position nor corollary discharge of a motor command for eye position has ever been demonstrated unambiguously in the cerebral cortex. We recently discovered the neuronal representation of proprioceptive eye position signal in monkey primary somatosensory cortex.