Abstract
BackgroundRepresenting one's own body is often viewed as a basic form of self-awareness. However, little is known about structural representations of the body in the brain.Methods and FindingsWe developed an inter-manual version of the classical “in-between” finger gnosis task: participants judged whether the number of untouched fingers between two touched fingers was the same on both hands, or different. We thereby dissociated structural knowledge about fingers, specifying their order and relative position within a hand, from tactile sensory codes. Judgments following stimulation on homologous fingers were consistently more accurate than trials with no or partial homology. Further experiments showed that structural representations are more enduring than purely sensory codes, are used even when number of fingers is irrelevant to the task, and moreover involve an allocentric representation of finger order, independent of hand posture.ConclusionsOur results suggest the existence of an allocentric representation of body structure at higher stages of the somatosensory processing pathway, in addition to primary sensory representation.
Highlights
Knowledge about the physical structure of our own body is a basic form of self-awareness
Our results suggest the existence of an allocentric representation of body structure at higher stages of the somatosensory processing pathway, in addition to primary sensory representation
We investigate how somatosensory codes become connected to body structure representation (BSR), by testing knowledge about tactile stimulation of the fingers in the absence of vision
Summary
Knowledge about the physical structure of our own body is a basic form of self-awareness. Notably touch, code basic features of sensory events at the skin, such as intensity and frequency These are represented in the somatotopic map of primary somatosensory cortex, which allows stimuli to be localised on the continuous sheet of the body surface. These primary representations do not contain structural information about the size and number of body parts themselves. The SI representation of the skin sheet does not respect the body’s true proportions, and decays rapidly in less than 1 second in the absence of sensory input [1,2] These properties reflect the needs of online sensory processing, but make them unsuitable for representing the body itself. Little is known about structural representations of the body in the brain
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