# Motor network organization in healthy development and chronic tic disorders

## TL;DR

The study explores how brain networks in children with tic disorders adapt to support motor control, revealing compensatory neural changes that differ from typical development.

## Contribution

The paper identifies compensatory neural adaptations in tic disorders that support motor control but not inhibition, using fMRI and dynamic causal modeling.

## Key findings

- TD patients show increased activation in ipsilateral motor and somatosensory regions during tasks.
- TD patients exhibit enhanced interhemispheric connectivity between parietal hubs.
- TD-related neural patterns deviate from typical developmental trajectories in motor regions.

## Abstract

Tic disorders (TD) are childhood-onset neurodevelopmental disorders characterized by sudden, repetitive motor and vocal tics, often with partial or complete remission by the time young adulthood is reached. We here investigated motor control and compensatory neural processes in drug-naïve children and adolescents with chronic Motor Tic Disorder or Tourette Syndrome (TD) by examining motor network activity and connectivity compared to healthy controls. Using a reaction time (RT) task under varying cueing conditions, combined with functional magnetic resonance imaging (fMRI) and dynamic causal modelling (DCM), we explored how TD-related motor networks adapt to support volitional movement control. Participants with TD demonstrated enhanced task accuracy across internally and externally cued conditions despite deficits in sustained motor inhibition (blink suppression). Relative to controls, individuals with TD exhibited increased task-related activation in ipsilateral motor regions, particularly in the primary motor cortex, and somatosensory cortex, and enhanced interhemispheric connectivity between parietal sensory-motor hubs. Notably, while in typically developing participants, age-related increases in parietal lobe activation and modulatory connectivity between primary motor and premotor regions were linked to improved task accuracy, working memory and visuomotor coordination, TD patients deviated from this normative developmental trajectory with distinct, atypical but neither delayed nor accelerated neural activation and connectivity patterns. Our data suggest that TD involves compensatory neuroplastic adaptations that leverage additional sensorimotor resources to improve motor control but do not extend to motor inhibition processes. Moreover, the findings emphasize the intricate interplay between motor control and neural plasticity in TD, highlighting how compensatory mechanisms may serve as adaptive responses to motor challenges. These findings open avenues for therapeutic strategies that harness the brain's compensatory capacities to enhance motor control and facilitate TD management.

Heinen et al. use functional MRI and dynamic causal modelling to study motor control in typically developing children and adolescents and drug-naïve patients with Tic Disorders. Patients exhibit distinct brain activation and connectivity patterns, reflecting compensatory adaptations that support reactive motor control but diverge from normative developmental trajectories.

Graphical Abstract