Evidence for normative intracortical inhibitory recruitment properties in cervical dystonia

Abstract Objective Dystonia is associated with reduced intracortical inhibition as measured by the cortical silent period (cSP); however, this may be due to abnormal cSP threshold or input-output properties. This study evaluated cSP recruitment properties in people with cervical dystonia (CD). Methods Bilateral electromyographic recordings were collected in the upper trapezius muscle in response to transcranial magnetic stimulation of the left and right primary motor cortex in a group with CD (n=19) and controls (n=21). cSP threshold, cSP input-output properties at stimulation intensities from 1 to 1.4x the cSP threshold, ipsilateral silent period duration (iSP) and timing and magnitude of the contralateral and ipsilateral motor evoked potential (MEP) were assessed. Results The cSP threshold, input-output properties, and contralateral MEP magnitude were not significantly different between groups (all p>0.07). Hemispheric symmetry was present in the control group while the CD group had reduced iSP (p Conclusions Recruitment properties of intracortical inhibition are similar between control and CD groups. Transcallosal inhibition is asymmetric between hemispheres in people with CD. Significance Evidence of normative intracortical inhibition recruitment properties challenge the commonly held view that cortical inhibition is reduced in dystonia.