Muscle theta activity in the pathophysiology of cervical dystonia

Abstract

Background: Increased theta-band intermuscular coherence (IMC) between neck muscles has been reported as pathophysiological features of cervical dystonia (CD). Objectives: investigate whether increased theta power and IMC are specific to the affected muscles, cortically driven, and actively contribute to dystonic contractions by examining the effect of sensory trick (ST) and analyzing correlations with clinical severity. Methods: 29 patients with torticollis (13 with effective ST) and 14 healthy subjects (HS) participated. We recorded EMG from bilateral sternocleidomastoid (SCM) and biceps (BIC) muscles and EEG over sensorimotor cortex. Theta power, IMC, and corticomuscular coherence (CMC) were analyzed across baseline and touch conditions and correlated with Torticollis Severity Scale (TSS) scores. Granger causality was used to assess the directionality of coherence. Results: patients exhibited increased theta power in SCMs but not in biceps muscles. Theta IMC was significantly higher only between bilateral SCMs in CD compared to HS. We found no group differences in theta CMC, with Granger causality indicating predominant theta connectivity from muscle to cortex. The ST was associated with increased theta IMC between SCMs, while patients without ST showed a significant reduction in IMC. SCM theta power and IMC were both inversely correlated with TSS. Conclusions: increased theta power and IMC in SCMs are specific to CD and likely reflect a subcortical drive rather than a cortical influence. Our results challenge prior suggestions of a pathogenic role for muscle theta synchronization in CD and suggest a possible compensatory role in balancing head position.

Keywords

• Cervical dystonia
• Pathophysiology
• Muscle activity
• Theta band synchronization
• Intermuscular coherence
• Corticomuscular coherence