Know thyself: behavioral evidence for a structural representation of the human body.
BACKGROUND
Representing 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.


RESULTS
We 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.


CONCLUSIONS
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.
Institute of Cognitive Neuroscience, University College London, London, United Kingdom.
Elena
E
Rusconi
Mirandola
M
Gonzaga
Michela
M
Adriani
Christoph
C
Braun
Patrick
P
Haggard
D000293:Adolescent; D000328:Adult; D001364:Awareness / Q000502:physiology*; D001828:Body Image; D005260:Female; D005385:Fingers / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D008960:Models, Psychological; D009484:Neuropsychology; D011187:Posture / Q000502:physiology; D012677:Sensation / Q000502:physiology*; D014110:Touch / Q000502:physiology; D055815:Young Adult