Clinical observations of patients with writer's cramp suggest that abnormal
ities of the sensory system may be a frequent finding in this disorder. Neu
rophysiological data from an animal model of focal dystonia have revealed c
ells in somatosensory cortex with enlarged and overlapping tactile receptiv
e fields. However, psychophysical studies so far have been unable to docume
nt a clinical correlate supporting a similar enlargement of receptive field
s in humans. We compared the fingertip discrimination of the orientation of
fine spatial gratings between writer's cramp and control subjects and foun
d a significant decrease in grating sensitivity in the patients, consistent
with the possibility of enlarged tactile receptive fields. In addition, we
duplicated previous experiments showing an abnormality of tactile temporal
discrimination. The results provide psychophysical measures which may rela
te to the development of sensory cortical reorganization in patients with w
riter's cramp.