Disaccoppiamento funzionale movimento-indotto dell'area motoria e sensitiva primaria nella distonia focale task-specifica dell'arto superiore: studio sperimentale magnetoencefalografico

Objective. Due to growing evidence of sensorimotor integration impairment in focal task-specific hand dystonia, we aimed at describing primary sensory (S1) and primary motor (M1) cortex source activities and their functional cross-talk during a non-dystonia-inducing sensorimotor task free of biases generated by the interfering occurrence of dystonic movements. Method. Magnetoencephalographic brain signals and opponens pollicis electromyographic activities were acquired at rest and during a simple isometric contraction performed either alone or in combination with median nerve stimulation. The task was performed separately with the right and left hand by 8 patients suffering from focal-task-specific-hand-dystonia and by 8 healthy volunteers. Through an ad-hoc procedure (Functional Source Separation), distinct sources were identified in S1 (FS_S1) and M1 (FS_M1) devoted to hand control. Spectral properties and functional coupling (coherence) between the two sources were assessed in alpha[8, 13]Hz, beta[14, 32]Hz and gamma[33, 45]Hz frequency bands. Results. No differences were found between spectral properties of patients and controls for either FS_M1 or FS_S1 cerebral sources. Functional coupling between FS_M1 and FS_S1 (gamma band coherence), while comparable between dystonic patients and healthy controls at rest, was selectively reduced in patients during movement. All findings were present in both hemispheres. Interpretation. Because previous literature has shown that gamma-band sensory-motor synchronisation reflects an efficiency index of sensory–motor integration, our data demonstrate that, in dystonic patients, uncoupling replaces the functional coupling required for efficient sensory–motor control during motor exertion. The presence of bi-hemispheric abnormalities in unilateral hand dystonia supports the presence of an endophenotypic trait.