Investigating the neural correlates and oscillatory dynamics of tics in Tourette Syndrome

335 

Abstract Submission 

Mairi Houlgreave¹, Aikaterini Gialopsou¹, Elena Boto¹, Matthew Brookes¹, Stephen Jackson¹

¹University of Nottingham, Nottingham, England

Mairi Houlgreave  
University of Nottingham
Nottingham, England

Aikaterini Gialopsou  
University of Nottingham
Nottingham, England

Elena Boto  
University of Nottingham
Nottingham, England

Matthew Brookes  
University of Nottingham
Nottingham, England

Stephen Jackson  
University of Nottingham
Nottingham, England

In Tourette syndrome (TS), tics are commonly preceded by a premonitory urge which is thought to be a negative reinforcer of tic expression, suggesting that tics may be a voluntary response to these sensations (Capriotti et al, 2014). Voluntary movements are associated with a desynchronisation of oscillations in the 8-30 Hz range, followed by a post-movement beta (13-30 Hz) rebound (PMBR) (Jurkiewicz et al, 2006; Pfurtscheller et al, 1996). Here, we explore the oscillatory changes within the primary motor cortex during tics and voluntary movements. We also investigate the oscillatory activity within the right insula and cingulate cortex, which have been shown to be involved in urge (Jackson et al, 2011). Tic expression during neuroimaging is most often required as an overt marker of increased urge, however this can lead to a loss of large amounts of data due to head movement. Therefore, our data were collected using Optically Pumped Magnetometer (OPM) magnetoencephalography (MEG) which uses head-mounted sensors (65 triaxial), allowing participant movement throughout the scan (Boto et al, 2018).

OPM-MEG data were acquired from 16 participants with TS (7F, mean age (±SD): 34.2 ±11.1 years). Participants were asked to complete two paradigms: the first paradigm involved sixty 10 second trials involving a single index finger abduction; the second paradigm involved 4 alternating 5-minute blocks of "Rest" and "Suppress" where participants were instructed to try to suppress their tics. Video of the participants' movements was recorded, during OPM-MEG, for offline analysis of tics. Trials were defined as 4 seconds in duration and began 2 seconds prior to tic bout onset.
Anatomical data (MPRAGE, 1mm isotropic) from these participants were used for linearly-constrained minimum variance beamforming (Robinson and Vrba, 1999). Timecourses were then weighted towards the central voxel for each brain region of the automated anatomical atlas, resulting in a single virtual electrode timecourse for each region. Data were standardized (Z-scored) after removal of bad channels and trials. Two datasets were excluded from both tasks due to poor data quality. Two further datasets were excluded from the voluntary movement task due to technical problems during data collection.

Analyses of the spectral timecourses of mu-alpha (8-12 Hz) and beta frequencies, from the contralateral motor cortex, demonstrated significant desynchronisation during the externally cued voluntary movements (Figure 1). However, there was no significant PMBR. In contrast, there was no significant desynchronisation at tic onset across the bilateral motor cortices (Figure 2). The mid-cingulate cortex and right insula showed no significant changes in mu-alpha and beta spectral timecourses before, or at tic onset.

Our finding of movement-related desynchronisation during volitional movements, but not tics, is in-line with previous research which describes desynchronisation of beta oscillations during voluntary movements using EEG, but no movement-related desynchronisation prior to tics (Morera Maiquez et al, 2022). Readiness potentials are not reliably seen before tics, despite a readiness potential being present before volitional movements (Obeso et al, 1981). Therefore, our data support the hypothesis that the oscillatory dynamics involved in tic generation differ from that of voluntary movement, suggesting that tics may be involuntary. The lack of significant changes in the 8-30 Hz range, in regions associated with urge, may be due to different regions of the insula having different roles (Kurth et al, 2010), suggesting that whole region analysis may not be ideal for identifying activity associated with urge. Regardless, OPM-MEG was shown to be capable of recording participants with TS during their tics where conventional methods such as EEG have previously shown artefacts associated with tic onset (Morera Maiquez et al, 2022).

Neurodevelopmental/ Early Life (eg. ADHD, autism) ¹

EEG/MEG Modeling and Analysis ²

MEG

Motor

Movement Disorder

Tourette's Syndrome