Sustained activation in basal ganglia and cerebellum after repetitive movement in cervical dystonia

Introduction: We previously observed abnormally sustained fMRI BOLD signal in the basal ganglia in focal hand dystonia (FHD) patients after they performed a repetitive finger tapping task. Focal hand dystonia is frequently a task-specific dystonia, where pathogenesis has been linked to excessive task repetition and aberrant sensorimotor plasticity. In the current study we asked if the effect of repetitive movement observed in FHD would be seen in other forms of dystonia where there is less known about the role of muscle use and repetition. Methods: We evaluated fMRI BOLD signal time courses before, during, and after the block design finger tapping task in cervical dystonia (CD) patients for comparison with our previous study of focal hand dystonia. To ask whether brain function differences in CD might be linked to aberrant cervical muscle function during the task, we acquired surface EMG (sEMG) from a subset of the CD patients and controls at a follow-up session. Specifically, we measured hand/arm and cervical muscle activity during the tapping task. Results: We observed abnormally sustained BOLD signal after tapping in CD participants in the left putamen and left cerebellum during non-dominant (left) hand tapping runs. BOLD signals in left putamen and cerebellum were also abnormally elevated in CD during the tapping task itself and escalated over time as the task was repeated. The laterality of sustained putamen signal was the same in CD as in our previously studied FHD cohort: patient/control differences were observed only in the left hemisphere. In contrast, there were no cerebellar BOLD time course abnormalities in the FHD cohort. sEMG signal across the left-hand tapping run bore strong resemblance to contralateral fMRI BOLD time courses at both the group and the individual level, including escalation of signal during tapping and sustained activity during rest blocks following tapping in CD. These effects were largest and most consistent in the right sternocleidomastoid (SCM) muscle. In contrast, task-related arm/hand muscle (flexor carpi radialis) sEMG was similar between CD and controls and did not escalate in either group. Discussion: Based on these preliminary, qualitative findings, we propose that future paired imaging/EMG studies in larger cohorts are needed to evaluate the link between brain abnormalities and aberrant, task-related function in the dystonic muscles. While the imaging findings are not inconsistent with sustained brain activity reflecting an endophenotype and/or hemodynamic abnormality in CD, the sEMG data support the additional possibility that in CD there is an amplified response to the normal mechanical demand of hand tasks on proximal/core body musculature.