The event related potential (ERP) technique is enjoying widespread application in neurophysiological research due to its fine temporal resolution. Of relevance to this study are ERPs related to voluntary movements. The precision with which movement related processes could be recorded using the ERP technique was demonstrated by Gilden, Vaughan and Costa (1966) and Kutas and Donchin (1974, 1977, and 1980) who found that the readiness potential (RP) immediately preceding hand movement was larger over the hemisphere contralateral to the responding hand. Given that left hemisphere controls right hand movements and vice versa, their findings confirmed that the lateralized readiness potential (LRP) is an index of motor preparation. It has been well established that electrodes from the left precentral site (C3) and from the right precentral site (C4) can capture LRPs, and that the motor cortex is the major generator of this component. In the speech domain, researchers recording ERPs related to motor preparation have often considered pre-determined electrode sites (e.g., F3, F4, C3, C4, Cz) assuming that their proximity to motor areas on the cortex enables capturing of specific activity from those areas [F3 close to Broca’s area, Cz close to Supplementary motor area (SMA), C3 to left motor strip, C4 to right motor strip]. A consistent finding has been that the RP preceding speech is greatest at the central electrode sites, which has been attributed to SMA and motor cortex activity. Studying speech production related ERPs at predetermined set of electrodes might not suffice for two reasons: (1) unlike simple finger movement, speaking is a fine motor skill requiring coordination of multiple systems (e.g., respiratory system, phonatory system, articulatory system) and muscles, and (2) the far-field nature of the ERP recording technique often results in spatial and temporal overlap of components. To overcome these challenges, this study considered multichannel recordings and principal component analysis (PCA). Twenty three healthy participants completed a simple hand motor task (pressing a button with the right index finger and another button using the left index finger based on the color of a stimulus frame displayed on a computer screen), and a speech task (saying “pool” or withholding the response based on the color of the frame). The purpose of including a hand motor task was to verify that neural activity specific to motor preparation was detectable in participants when a well-established condition for the elicitation of LRPs was utilized. Both stimulus-locked and response-locked ERPs from 21 right handed participants (11 females and 10 males) were studied. Interhemispheric difference wave analysis and PCA revealed left hemisphere lateralization of the potential (i.e., the LRP) immediately preceding right hand movements, similar to previous studies. The LRP specific to left hand movements (non-dominant hand), however, showed bihemispheric distribution. Results from the speech motor task confirmed that overlapping components affect interpretation of ERPs related to speech production if just central electrode sites are considered. Two ERP components emerged from the multichannel PCA as distinguishing between the speaking and no speaking condition: a posterior negative component and a left lateralized positive component. The morphology of the posterior negative component and significant moderate correlation of its amplitude with the mean reaction time suggest that this component is a possible index of speech motor preparation. Further research is required to determine whether the left-lateralized component reflects a process mediated by the speech dominant hemisphere (left). In addition to demonstrating the usefulness of multichannel recordings and PCA in ERP investigations, the study provides several methodological guidelines for capturing ERPs related to speech production.

Les troubles des tics, comme le syndrome de Gilles de la Tourette et le trouble de tics chroniques, sont des conditions neuropsychiatriques impliquant des tics moteurs et/ou phoniques. En plus de nombreuses comorbidités, les patients qui en sont atteints ont aussi des difficultés neuropsychologiques, notamment au niveau de l’inhibition et des fonctions motrices. La thérapie cognitivo-comportementale permet d’améliorer les tics et la condition générale de ces patients. Nous avons donc enregistré, durant une tâche de compatibilité stimulus-réponse, les potentiels évoqués cognitifs et les potentiels de latéralisation motrice (lateralized readiness potential; LRP) chez 20 patients atteints de trouble des tic avant et après une thérapie cognitivo-comportementale, et chez 20 participants contrôles. Chez les patients atteints de trouble des tics, nos résultats ont révélé une apparition plus tardive de l’amorce du LRP moyenné par rapport au stimulus, une amplitude plus élevée du LRP moyenné par rapport à la réponse, et une suractivation frontale liée aux processus d’inhibition. Suite à la thérapie, le retard au niveau de la latence de l’amorce du LRP moyenné par rapport à la réponse est comblé et l’amplitude du LRP moyenné par rapport à la réponse est normalisée, mais pas la suractivation frontale liée à l’inhibition. Cela suggère donc que la thérapie induit une modification des processus prémoteurs de sélection et de préparation de la réponse, ainsi que des processus d’exécution motrice, mais n’altère pas la suractivation frontale reliée aux fonctions inhibitrices. Étant donnés ces résultats, nous suggérons que la thérapie cognitivo-comportementale induit une modification du fonctionnement des aires motrices du cerveau. / Gilles de la Tourette syndrome and chronic tic disorder are two neuropsychiatric condition involving motor and/or phonic tics. In the DSM, these two conditions are characterized as “tic disorders”. Patients with such diagnoses face numerous comorbidities, and also show multiple neuropsychological impairments, especially concerning inhibition and motor processing. Tic symptoms, as well as general condition, can be improved with a cognitive-behavioural therapy (CBT). To this end, we recorded, during a stimulus-response compatibility task, event-related potentials and lateralized readiness potentials in 20 patients with tic disorder and 20 healthy controls. Patients and controls were paired on age, sex and hand dominance. Our result revealed a delay in stimulus-locked lateralized readiness potential (LRP) onset latency, higher response-locked LRP peak amplitude and a frontal overactivation related to stimulus inhibition in GTS and CTD patients. Following CBT, stimulus-locked LRP onset latency and response-locked LRP peak amplitude were normalized, but the frontal overactivation related to inhibition processing remained unchanged. These results suggest that CBT induces a modification of pre-motor processes such as response selection and preparation, as well as motor processes like response execution, but does not affect cortical activation related to stimulus inhibition. Since we found a reduction in tic symptoms, as well as a normalization of stimulus-locked LRP onset latency and response-locked LRP peak amplitude, and because LRPs are partly generated by the supplementary motor area, we suggest that CBT leads to a modification of this structure’s functioning.