In Addition to Differential Activation of Primary and Secondary Sensorimotor Areas Which

e-Discussion

In addition to differential activation of primary and secondary sensorimotor areas which are discussed in the main manuscript, we found an increased activation of the thalamus, caudate nucleus, prefrontal association cortex as well as the superior and medial temporal cortices in patients with ED compared to healthy controls (see Table 2 and Figure 2).

A hyperactivity of the basal ganglia (including the caudate nucleus)and thalamus has also been shown by PET and fMRI studiesduring rest e1-e3and motor executione4, e5 in patients with other forms of dystonia. It has been suggested that basal-ganglia-thalamic overactivity represents a faulty inhibitory control of the basal ganglia with an abnormal modulation of the direct cortico-striato-pallido-thalamo-cortical circuit. Within this concept, overactive direct inhibitory projections to the pallidum could release pallidal inhibition onto thalamo-cortical projections resulting in an overshoot of motor outpute3.

Increased activity of prefrontal and anterior insular association cortices has been reported in several studies examining motor tasks in patients with idiopathic torsion dystoniae5, e6, acquired hemidystoniae7 and writer’s crampe8. It has been argued that these results could represent a compensatory mental effort for achieving adequate task performance despite an interference with dystonia. Nevertheless, reduced prefrontal activity was shown in patients with other movement disorders (e.g. Parkinson disease) that could be assumed to experience comparable difficulties when performing similar motor tasks e9, e10. To some extent,prefrontal overactivity therefore appears to be an intrinsic abnormality in patients with dystonia, possiblydue to an overactivity of basal ganglia-prefrontal loops during movement preparation and planning. This interpretation is underlined by thesimilar observation ofprefrontal and insular overactivity in our ED patients even during the ‘neutral’ task when they experience neither dystonic symptoms nor performance deficits.

We also found an overactivity within bilateral superior and middle temporal, i.e. primary and secondary auditory cortices during both,the ‘mouthpiece’ and the ‘neutral’ task in the patient group. Brass playing and musical performance generally involve anintense interplay between motor coordination (i.e. forming the embouchure and controlling the airflow) and somatosensory as well as auditory feedback (tone pitch, quality and sound intensity).Therefore it is conceivable that ED patientsmore strongly rely on auditory feedback than healthy musicians due to their deficits in motor coordination. This could lead to compensatorily intensified auditory processing or auditory imagerye11, e12, particularly when considering the mismatch between the expected, but strongly reduced auditory feedback during the fMRI experiment.On the other hand, strong transmodal connections have been demonstrated in musicians bi-directionally linking primary and secondary sensorimotor with auditory activitye13-e17.Stronger auditory activation in ED patients accompanying cortical sensorimotor overactivity could therefore directly reflect an increase oftop-down motor-auditory connectivity.

e-References:

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