Parieto-motor cortical dysfunction in primary cervical dystonia

Dystonia is considered as a motor network disorder involving the dysfunction of the posterior parietal cortex, a region involved in preparing and executing reaching movements.

We used transcranial magnetic stimulation to test the hypothesis that cervical dystonic patients may have a disrupted parieto-motor connectivity.

We enrolled 14 patients with primary cervical dystonia and 14 controls. A paired-pulse transcranial magnetic stimulation protocol was applied over the right posterior parietal cortex and the right primary motor area. Changes in the amplitudes of motor evoked potential were analyzed as an index of parieto-motor effective connectivity. Patients and healthy subjects were also evaluated with a reaching task. Reaction and movement times were measured.

In healthy subjects, but not in dystonic patients, there was a facilitation of motor evoked potential amplitudes when the conditioning parietal stimulus preceded the test stimulus applied over the primary motor area by 4 ms. Reaction and movement times were significantly slower in patients than in controls. In dystonic patients, the relative strength of parieto-motor connectivity correlated with movement times.

Parieto-motor cortical connectivity is impaired in cervical dystonic patients. This neurophysiological trait is associated with slower reaching movements.