Perceptual distortions of the human body image produced by local anaesthesia, pain and cutaneous stimulation
Knowledge of the size and orientation of the hand is essential if it is to be moved accurately in space. We used two psychophysical methods to determine whether the perceived size of a body part changes when its sensory input is changed: first, the selection of scaled drawings which matched the appa...
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Veröffentlicht in: | The Journal of physiology 1999-01, Vol.514 (2), p.609-616 |
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Sprache: | eng |
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Zusammenfassung: | Knowledge of the size and orientation of the hand is essential if it is to be moved accurately in space. We used two psychophysical
methods to determine whether the perceived size of a body part changes when its sensory input is changed: first, the selection
of scaled drawings which matched the apparent size of a body part, and second, a motor task in which the subject drew the
body part to depict its perceived size.
Complete anaesthesia of the thumb (with a digital nerve block) significantly increased its perceived size by 60â70% when assessed
with both psychophysical methods. During this anaesthesia, the perceived size of the adjacent index finger or digits on the
contralateral side was unaltered. However, the size of the unanaesthetized lips increased (by â¼50%).
Marked sensory loss for the lips (produced by topical anaesthetics) significantly increased their perceived size when assessed
with both methods of measurement. There was a small increase in apparent size of the thumb.
To determine whether changes in perceived size could also be produced by an elevation of peripheral inputs, innocuous electrical
stimulation of the digital nerves and also painful cooling of the digit were used. Both procedures produced small but significant
increases in perceived size of the stimulated part.
The results highlight lability in the perceived size of parts of the body and how this affects motor output. The data may
reveal perceptual consequences of acute changes in central somatosensory maps, changes which are known to occur with deafferentation. |
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ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1111/j.1469-7793.1999.609ae.x |