Cortical inhibitory function in cervical dystonia.

OBJECTIVE: To assess the specificity of cortical inhibitory deficits in cervical dystonia patients.

METHODS: A systematic test battery was developed to assess spatial and temporal aspects of cortical inhibition, in motor and somatosensory systems of the hand. We tested 17 cervical dystonia (CD) patients and 19 controls assessing somatosensory spatial inhibition (grating orientation test, interdigital feedforward subliminal inhibition), somatosensory temporal inhibition (temporal discrimination threshold, feedforward subliminal inhibition), motor spatial inhibition (surround inhibition), and motor temporal inhibition (short interval intracortical inhibition).

RESULTS: A significant deficit in CD was observed in both measures of somatosensory spatial inhibition, with a trend in the same direction in our measure of motor spatial inhibition. We found no significant group differences in temporal inhibition measures. Importantly, statistical comparison of effect sizes across the different measures showed that deficits in tests of spatial inhibition were greater than those in tests of temporal inhibition.

CONCLUSION: Our results suggest that CD is associated with abnormal function of local inhibitory cortical circuits subserving spatial sensory processing. Importantly, this abnormality relates to the somatotopic representation of an unaffected body part.

SIGNIFICANCE: These results clarify the nature of deficits in cortical inhibitory function in dystonia.