Somatosensory perception-action binding in Tourette syndrome

Abstract

It is a common phenomenon that somatosensory sensations can trigger actions to alleviate experienced tension. Such "urges" are particularly relevant in patients with Gilles de la Tourette (GTS) syndrome since they often precede tics, the cardinal feature of this common neurodevelopmental disorder. Altered sensorimotor integration processes in GTS as well as evidence for increased binding of stimulus- and response-related features ("hyper-binding") in the visual domain suggest enhanced perception-action binding also in the somatosensory modality. In the current study, the Theory of Event Coding (TEC) was used as an overarching cognitive framework to examine somatosensory-motor binding. For this purpose, a somatosensory-motor version of a task measuring stimulus-response binding (S-R task) was tested using electro-tactile stimuli. Contrary to the main hypothesis, there were no group differences in binding effects between GTS patients and healthy controls in the somatosensory-motor paradigm. Behavioral data did not indicate differences in binding between examined groups. These data can be interpreted such that a compensatory "downregulation" of increased somatosensory stimulus saliency, e.g., due to the occurrence of somatosensory urges and hypersensitivity to external stimuli, results in reduced binding with associated motor output, which brings binding to a "normal" level. Therefore, "hyper-binding" in GTS seems to be modality-specific.

Figure 1

Behavioral data (inverse efficiency score) demonstrating the interaction of Response × Finger compatibility for GTS patients (A) and healthy controls (B). The IES is illustrated separately for GTS patients (A) and healthy controls (B) for response repetition and response alternation in the feature (finger) repetition (FeatRep) condition and the feature (finger) alternation (FeatAlt) condition. Error bars represent the standard error of the mean (SEM).

Figure 2

Illustration of the experimental setup (electrode placement). Stimulation was applied via adhesive surface electrodes attached to (A) the back of the left hand, (B) the back of the right hand and (C) the palmar side of the thumb and little finger of the right hand. Responses were given by pressing the left or right control key with the respective index finger.

Figure 3

Schematic illustration of the experimental procedure. For clarity, one black dot represents a pair of electrodes. Electro-tactile stimuli were either applied to the thumb or little finger (5th digit) using a double (2 à 6 Hz) or quadruple (4 à 12 Hz) pulse. Details concerning stimulus and response timing can be found in “Materials and methods” section.