Abstract
In task-specific focal hand dystonia (tspFHD), the temporal dynamics of cortical activity in the motor system and how these processes are related to impairments in sensory and motor function are poorly understood. Here, we use time-frequency reconstructions of magnetoencephalographic (MEG) data to elaborate the temporal and spatial characteristics of cortical activity during movement. A self-paced finger tapping task during MEG recording was performed by 11 patients with tspFHD and 11 matched healthy controls. In both groups robust changes in beta (12–30 Hz) and high gamma (65–90 Hz) oscillatory activity were identified over sensory and motor cortices during button press. A significant decrease [p < 0.05, 1% False Discovery Rate (FDR) corrected] in high gamma power during movements of the affected hand was identified over ipsilateral sensorimotor cortex in the period prior to (−575 ms) and following (725 ms) button press. Furthermore, an increase (p < 0.05, 1% FDR corrected) in beta power suppression following movement of the affected hand was identified over visual cortex in patients with tspFHD. For movements of the unaffected hand, a significant (p < 0.05, 1% FDR corrected) increase in beta power suppression was identified over secondary somatosensory cortex (S2) in the period following button press in patients with tspFHD. Oscillatory activity within in the tspFHD group was however not correlated with clinical measures. Understanding these aberrant oscillatory dynamics can provide the groundwork for interventions that focus on modulating the timing of this activity.
Highlights
Task-specific focal hand dystonia is a debilitating movement disorder characterized by involuntary co-contractions of agonist and antagonist muscles of the hand and forearm during specific, well-learned activities such as playing a musical instrument, writing, or typing (Fahn et al, 1998)
At the sensor-level, time-frequency analyses show that around button press (0 ms; Figure 1) significant reductions in beta (∼20 Hz) power and increases in high gamma (∼80 Hz) power occur over MEG channels contralateral to the hand being used (Figure 1)
Localized activity can be identified in the source space analyses, where both subjects with Task-specific focal hand dystonia (tspFHD) and healthy controls demonstrated consistent beta band (12–30 Hz) power decreases bilaterally and high gamma (65–90 Hz) power increases contralaterally across the motor cortices (M1, premotor cortex (PMC)) around movement onset (0 ms; Figure 2)
Summary
Task-specific focal hand dystonia (tspFHD) is a debilitating movement disorder characterized by involuntary co-contractions of agonist and antagonist muscles of the hand and forearm during specific, well-learned activities such as playing a musical instrument, writing, or typing (Fahn et al, 1998). While the etiology of tspFHD is considered idiopathic, most researchers and clinicians agree focal dystonia is a multifactorial disorder developing from an interaction of both extrinsic (e.g., trauma, injury to the upper extremity, neuropathy, stress, perfectionism, poor ergonomics and/or repetitive overuse; Jankovic, 2001; Jabusch et al, 2004), and intrinsic factors (e.g., genetics, musculoskeletal limitations, neurophysiological abnormalities, personality; Gasser et al, 1998; Breakefield et al, 2008). It is not clear whether intrinsic factors predispose individuals to developing tspFHD or whether the observed aberrations in intrinsic features represent the consequences of the disorder. Brain mapping modalities that interrogate cerebral blood flow can only provide a static image of activity during a motor behavior, and lack the temporal fidelity to track changes in the brain that occur during discrete stages of movement
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