Subjective image of invisible hand coded by monkey intraparietal neurons.

Humans can perform purposeful hand actions even blindly in the dark, perhaps using mental images of the hand. To demonstrate such subjective body images, this study describes the activities of bimodal (somatosensory and visual) neurons in the monkey intraparietal cortex. Visual stimuli moving into the space encompassing their somatosensory receptive fields (s-RFs) on the hand activated these neurons, forming visual receptive fields (v-RFs) as if coding a hand-image. After the hand was hidden by covering it with an opaque plate, the v-RF persisted over the plate above the invisible s-RF. Furthermore, when the hand was moved invisibly under the plate, the v-RF moved over the plate to follow the invisible s-RF. Thus, monkeys can maintain and update subjective body images in the mind, and they are coded by intraparietal bimodal neurons.