Induced tic-like behavior in typically developed controls versus tics in Tourette syndrome

Abstract

The Gilles de la Tourette Syndrome (GTS) is a chronic neuropsychiatric disorder characterized by motor and vocal tics. Tics are sudden, repetitive movements or vocalizations, such as eye blinking or throat clearing. In patients with GTS, there are inter- and intra-individual differences with regard to the affected body regions, the number, frequency and severity of the tics. Some patients with GTS are affected by coprolalia, a complex vocal tic in which taboo words or inappropriate expressions are uttered. The occurrence of normally suppressed behavior in the form of tics raises the question of whether cognitive control mechanisms are altered in GTS. Previous studies often focused solely on the motor aspects of tics and provided inconclusive results. Since speech production also involves internal monitoring mechanisms of cognitive control, the present study examines the inhibition of slips of the tongue, including taboo words, at the linguistic level to investigate potential changes in cognitive control mechanisms in GTS.

For the study, the “Spoonerisms of Laboratory Induced Predisposition” (SLIP) paradigm was used, in which several pairs of inductor words with the same initial phonemes are presented, followed by a target word pair with inverse initial phonemes that should be pronounced aloud. This task created a conflict between two competing speech plans: the correct target word pair and the erroneous speech plan with the inverted phonemes, a so-called spoonerism. To induce a stronger conflict in the speech production process, taboo words were implemented as potential spoonerisms in addition to neutral words. During the task, participants’ brain activity was measured using electroencephalography (EEG) to identify the neural correlates of cognitive control triggered by the conflict.

The aim of the study was to investigate the conflict processes between the neutral and taboo condition at behavioral and electrophysiological levels in a typically developed control group (TDC) and in patients with GTS. It was hypothesized that patients with GTS would produce more spoonerisms, particularly taboo spoonerisms, due to altered cognitive control processes. Additionally, it was expected that the electrophysiological correlates of conflict monitoring would differ between the neutral and taboo conditions and that these would be more pronounced in the GTS group for correct responses. For the TDC group, it was anticipated that results from previous SLIP studies would be replicated. This means it was expected that fewer taboo spoonerisms would occur, as these would be more strongly suppressed, which is also associated with delayed onset times of correct vocalized responses in this condition.

The behavioral data showed differences between the neutral and taboo conditions. In both groups, the taboo condition was associated with a lower occurrence of spoonerisms and a delayed speech onset. From the EEG data, event related potentials (ERPs) time-locked to the speech prompt were calculated, which revealed that the neutral and taboo conditions were processed differently in the GTS group. This difference was most pronounced at the midline electrodes during a time window from 250 ms to 400 ms after the speech prompt. Additionally, a gradual recruitment of cognitive control processes depending on the number of inductor word pairs is indicated. This effect in the ERP data was not found in the TDC group.

The results show that the behavioral data for both GTS and TDC groups were similar, with differences observed between neutral and taboo conditions in both groups. In terms of neural processes for conflict monitoring, the GTS group exhibited increased activity in the conditions involving implicit taboo words. These different activation patterns between neutral and taboo words suggest distinct cognitive control processes during the monitoring of speech plans in the GTS group. These findings provide an important basis for future studies focusing on the neurolinguistic control mechanisms in speech production within the context of GTS.