406
there is overlap of the receptive fields so that the same sensory populations respond to two
different fingers, we do not necessarily expect linearity, because the metabolic demands of
a single population stimulated by two different fingers may be determined by a complex
function of the stimulus strength.
BOLD contrast was measured with fMRI during tactile stimulation of the index finger,
the middle finger, or both simultaneously in five patients with focal dystonia and seven
control subjects. In the control subjects, a linear combination of activation patterns for
individual finger stimulation predicts an average of 88 per cent of the variance in the pat-
tern of activity for combined stimulation. In patients with dystonia, the linear combination
predicted only 70 per cent of the combined stimulation pattern (p0.008; Figure 26.6).
Therefore, our results suggest that in patients with dystonia, the same region of sensory
cortex may respond to tactile stimuli on more than one finger. Disorganization of sensory
representations appears to be part of the pathophysiology of focal dystonia and may con-
tribute to motor abnormalities. Hence, emphasis needs to be placed in the sensory as well
as on the motor aspects of skill acquisition and practice in musicians. Perhaps all instru-
mentalists should learn Braille to enhance the functional segregation of individual fingers
and minimize the risk of dystonia.
Conclusion
Tools are now available to study the neurophysiological correlates of skill learning in
humans. The motor cortex plays an important role in motor skill learning, but so does the
sensory cortex. The sensorimotor cortex changes as a consequence of skill acquisition.
These plastic changes, which probably include functional and structural components, place
the subjects at great advantage for skillful task performance, but harbour the risk of the
development of motor control disorders. The results of our studies may be useful in under-
standing not only the physiology of skill acquisitions, but also the pathophysiology of
movement disorders in skilled performers. Further work along these lines may lead to help-
ful insight into the appropriate teaching/learning technique for fine motor skills.
Acknowledgements
Part of the work summarized in this chapter was done in collaboration with Mark Hallett,
Nguyet Dang, Leonardo Cohen, José María Tormos, Josep Valls-Solé, Terrance Sanger,
Gottfried Schlaug, Daniel Tarsy, Jesus Pujol, and Jaume Roset-Llobet. This work was sup-
ported in part by the General Clinical Research Center at Beth Israel Deaconess Medical
Center (National Center for Research Resources MO1 RR01032) and grants from the
National Institute of Mental Health (MH57980 and MH60734) and the National Eye
Institute (EY12091).
References
1.Critchley, M.and R. A. E. Henson(1977) Music and the Brain: Studies in the Neurology of Music.
Southampton: The Camelot Press.