Objective: To evaluate whether decreased lateralization of fine motor actions is an endophenotypic trait in adults with Tourette syndrome (TS), and whether it is related to inter-hemispheric connections.

Background: Youth with Tourette syndrome (TS) exhibit, compared to healthy, decreased ability to lateralize digital sequential tasks.

Methods: Thirteen adult TS patients (mean age 33.8 years) and 15 healthy volunteers (mean age 28.6 years, p>0.05) underwent: 1) a finger opposition task, performed with the right hand (RH) only or with both hands, using a sensor-engineered glove in synchrony with a metronome at 0.5 and 2 Hz; we calculated a lateralization index [(single RH – bimanual RH)/single RH X 100) for percentage of RH correct movements (%CORR), touch duration and inter-tapping interval; 2) MRI-based diffusion tensor imaging of inter-hemispheric corpus callosum (CC) connections between supplementary motor areas (SMA) and primary motor cortices (M1) and SMA-putamen connectivity.

Results: We did not detect significant between-group differences in structural organization of SMA-SMA and M1-M1 CC tracts, as well as of SMA-putamen fibre tracts. We confirmed a significant increase in the %CORR in the bimanual vs. single RH task in TS patients (p<0.001), coupled to reduced ability to lateralize finger movements (significantly lower lateralization index for %CORR in TS patients, p=0.04). The %CORR lateralization index correlated positively with tic severity measured with the Yale Global Tic Severity Scale (R=0.55;p=0.04). In healthy subjects, the %CORR lateralization index correlated positively with fractional anisotropy of SMA-SMA fibre tracts (R=0.63, p=0.02); this correlation was absent in TS patients.

Conclusions: TS patients exhibit a reduced ability to lateralize finger movements in sequential tasks across different ages. In TS patients, the ability to lateralize fine motor actions may be influenced by plastic adaptive changes in brain regions different from inter-hemispheric fibre tracts, and could be related to self-regulatory mechanisms associated with tic suppression.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/lateralization-of-fine-motor-actions-in-tourette-syndrome-persisting-through-adulthood/