Tactile processing and vibrotactile discrimination capacity in children with tourette syndrome

Tourette Syndrome (TS) is a childhood-onset developmental psychiatric disor- der. Pediatric patients are diagnosed with TS if they show multiple motor tics and at least one vocal tic for at least one year. The tic severity is known to be reduced in most of the cases as the patient progress into adulthood which suggests a cerebral adapta- tion over time. The pathology of TS is not clear; however, neurotransmission deficits, especially of γ-aminobutyric acid (GABA), and structural alterations in the cerebral structures are believed to be play a role in disorder's occurrence. Existing literature suggests the tics to arise from hyperexcitability due to GABAergic dysfunction, and the adaptive somatosensory mechanisms in TS to be disrupted. This study aimed to extend the GABAergic adaptive dysfunction in TS hypothesis by assessing the detec- tion and difference thresholds through a psychophysical vibrotactile battery. Thirty TS children (7 female, 23 male) and 25 healthy controls (7 female, 18 male) participated in the experiments. Vibrotactile stimuli were generated by a portable device and applied to the fingertips of the subjects. The vibrotactile battery consisted of Choice Reaction Time (cRT, amplitude: 200 μm, Static Detection Threshold (DT_s ), Dynamic Detec- tion Threshold (DT_c , amplitude ramp: 2 μm/s ), Amplitude Discrimination (AD, standard stimuli: 50, 100, 200 μm ), and Amplitude Discrimination with single-site adaptation (cAD, the same standards, adapting stimuli: 100, 300 μm, adaptation dura- tion: 1 s) measurements. The analyses showed that both groups produced comparable detection thresholds. Amplitude discrimination tasks produced further support for the GABAergic adaptive dysfunction in TS hypothesis, since in the baseline AD tasks TS group produced significantly higher difference thresholds, and in the cAD tasks control group closed the gap by showing a more prominent adaptation.