Deficient modulation of oscillatory brain activity in focal hand dystonia

Background: Control of dexterous motor function requires, depending on the context, not only retrieval but also adequate non-retrieval of acquired motor programs. There is evidence that this contextual control is associated with bidirectional modulation of oscillatory neuronal activity in the alpha band in a fronto-central network. Retrieval of learned motor programs is associated with task-related coupling and voluntary non-retrieval (suppression) with decoupling in this network. Here, we evaluate bidirectional modulation of oscillatory neuronal activity during contextual control of movements in patients with focal hand dystonia (DYST).

Methods: 12 DYST were studied (6f;42.1y±10.2SD). Oscillatory activity was assessed with analysis of multichannel surface EEG. DYST were asked to overlearn a complex finger movement sequence the day before the experiment. The sequence consisted of 16 key presses; the rhythm of 1Hz was triggered by visual cues without information about which key had to be pressed. EEG was recorded while participants executed (ACT, retrieval) or suppressed (INH, non-retrieval) the learned motor actions due to the contextual constraints. Task-related phase coherence (TRPhCoh) was calculated for the alpha band (10–13Hz). The difference of TRPhCoh to unconstraint rest was calculated for ACT and INH. Positive values of TRPhCoh denote an increase of coupling compared to rest, negative values represent decoupling. One-sample t-tests were calculated for each electrode pair and separately for ACT and INH to test for significant (p<.01) deviation from 0 over the sample of DYST.

Results: DYST showed a normal pattern of TRPhCoh increase during ACT (retrieval) in a fronto-central cortical network involved in execution of learned motor programs comparable to healthy subjects. During INH (non-retrieval) healthy subjects showed pronounced decoupling in the same network (reduced TRPhCoh compared to rest). In contrast to the findings in healthy subjects, DYST did not exhibit such a pattern of decoupling during contextual non-retrieval (suppression) of learned motor programs.

Conclusions: These data provide evidence for the absence of adequate bidirectional modulation of oscillatory activity during control of acquired motor programs, especially in a situation in which motor programs have to be inhibited. These findings support the hypothesis of deficient contextual inhibitory control in the sensorimotor system as one potential underlying mechanism in focal dystonia.