Probing the inhibitory motor circuits in adductor laryngeal dystonia during a dystonia-unrelated task.

BACKGROUND:The pathophysiology of adductor laryngeal dystonia (AdLD) remains unknown; however, there is growing evidence that dystonia is associated with disruptions in the inhibitory regulation of sensorimotor cortical areas. Using functional MRI (fMRI) and transcranial magnetic stimulation (TMS) complementarily, we previously demonstrated an overly activated laryngeal motor cortex and revealed correlations between blood-oxygen-level dependent (BOLD) activation and intracortical inhibition in a phonation (dystonia-related) task in adductor laryngeal dystonia (AdLD). OBJECTIVE:Here, we aimed to characterize the brain-based findings in the primary motor cortex (M1) during a dystonia-unrelated (finger tapping) task in AdLD and controls (CTL). METHODS:We examined the between-group differences in task-dependent BOLD activation and intracortical inhibition, measured by the TMS-evoked cortical silent period (cSP), in the M1. The correlations between fMRI and TMS responses were assessed. RESULTS:There is more broadly dispersed BOLD activation, not confined to the hand motor cortex, and reduced intracortical inhibition in AdLD compared to CTL. Further, there are more positive correlations between cSP and BOLD activation in a task unrelated to dystonic symptoms in AdLD compared with CTL. This is in contrast to our previous work that demonstrated fewer positive correlations in AdLD during a dystonic phonation task. CONCLUSIONS:In unaffected musculature activation, there is dispersed BOLD activation that is correlated with intracortical inhibition suggesting a possible compensatory strategy in the non-dystonic muscles.