Proceedings of The Physiological Society

University College London December 2005 (2006) Proc Physiol Soc 1, PC5

Poster Communications

Sensorimotor re-organisation is different in musicians dystonia and writers cramp

Rosenkranz, Karin; Butler, Katherine; Williamon, Aaron; Carla, Cordivari; Lees, Andrew; Rothwell, John;

1. Institute of Neurology, London, United Kingdom. 2. Devonshire Hospital , London, United Kingdom. 3. Royal College of Music, London, United Kingdom.

Musicians dystonia (MD) and writers cramp (WC) are both focal hand dystonias. However, in a recent study we found that despite their similarities, there were differences in pathophysiology that may relate to differences in their history of hand use. We examined the pattern of sensorimotor organisation (SMO) in the motor cortex by applying transcranial magnetic stimulation (TMS) during vibration of an intrinsic hand muscle (80 Hz) using a small probe placed over the muscle belly. In healthy non-musicians (HS), vibration of a single hand muscle (e.g. abductor pollicis brevis, APB) increases the excitability of corticospinal outputs to the vibrated muscle, whilst having the opposite effect on the non-vibrated hand muscles (e.g. first dorsal interosseous, FDI; abductor digiti minimi, ADM) [1]. SMO was abnormal in both patient groups. However, the abnormality was different in each: corticospinal excitability was not influenced by vibration in WC, whereas in MD vibration of APB increased corticospinal excitability to all hand muscles. In the healthy musicians (HM), a control group that we used to test for physiological adaptation of the brain to musical training, APB vibration increased output to APB and FDI but not ADM, an organisation intermediate between that of HS and MD. The hypothesis is that musical practice in HM leads to beneficial changes in motorcortical organisation, but in MD these progress too far and begin to interfere with movement rather than assist it. In WC sensory information from the hand may have a smaller influence [1]. In the present experiments we tested whether SMO is flexible. We gave 15 min vibration discontinuously to the APB whilst subjects either attended to (ATT+) or diverted attention from (ATT-) the stimulation. In HS, 15 min ATT+ led to an expansion of the effect of subsequent short term APB vibration so that it facilitated both APB and FDI. Conversely ATT- abolished the subsequent effect of short term APB vibration on all muscles. In HM, ATT+ tended to re-establish the normal facilitatory effect of short term APB vibration onto APB and suppress its facilitation of FDI. Conversely, ATT- reduced the co-facilitatory effect on APB and FDI. In MD ATT+ strengthened the coactivation of APB and FDI, while ATT- failed to have any effect on SMO. Finally in WC none of the interventions influenced SMO. We conclude that in HS and HM the SMO is a flexible input-output organisation that is influenced by long periods of sensory input and by the focus of attention. However, in MD the flexibility of SMO is reduced. Impaired adaptability in the circuits responsible for SMO might mark the transfer from beneficial adaptation towards maladaptation in HM versus MD. The finding in WC that both interventions failed to induce any SMO changes suggests that they have a more generalised impairment of central sensory integration.

Where applicable, experiments conform with Society ethical requirements