Objective. This study aims to investigate alterations of brain connectivity using multivariate electroencephalographic data to provide new insights of the brain connectivity dynamics of dystonia. Approach. We recorded electroencephalography (EEG) of patients with right upper limb idiopathic focal dystonia and paired controls during resting state, writing-from-memory, and finger-tapping tasks. We applied power spectrum analyses considering the mu, beta and gamma rhythms of the motor cortex and analyzed brain connectivity networks and microstates (MS). Main results. The power spectra results showed that patients had a loss of desynchronization of the beta rhythm during the writing task. We observed differences in the structure of the connective core in beta rhythm, as well as, in the intensity of the patient’s hubs observed with basis in path length measures in mu and beta rhythms. Abnormalities were also identified in MS of default mode networks of patients associated with its performances during motor tasks. Significance. The EEG connectivity analyses provided interesting insights about the cortical electrophysiological patterns in dystonia, such as loss of event-related desynchronization, changes in the effective connectivity with similar signature to other neurological diseases, indications of alterations in the default-mode-network. Our findings are consistent with previously described connectivity abnormalities in neuroimaging studies confirming that dystonia is a network disorder.

Significance: Dystonia is a dynamic and complex disorder. Real-time analysis of brain activity during motor tasks may increase our knowledge on its pathophysiology. Functional near-infrared spectroscopy (fNIRS) is a noninvasive method that enables the measurement of cortical hemodynamic activity in unconstrained environments. Aim: We aimed to explore the feasibility of using fNIRS for the study of task-related brain activity in dystonia. Task-related functional magnetic resonance imaging (fMRI) and restingstate functional connectivity were also analyzed. Approach: Patients with idiopathic right-upper limb dystonia and controls were assessed through nonsimultaneous fMRI and fNIRS during a finger-tapping task. Seed-based connectivity analysis of resting-state fMRI was performed in both groups. Results: The fMRI results suggest nonspecific activation of the cerebellum and occipital lobe in dystonia patients during the finger-tapping task with the affected hand. Moreover, fNIRS data show lower activation in terms of oxyhemoglobin and total hemoglobin in the frontal, ipsilateral cortex, and somatosensory areas during this task. In dystonia, both fMRI and fNIRS data resulted in hypoactivation of the frontal cortex during finger tapping with both hands simultaneously. Resting-state functional connectivity analysis suggests that the cerebellar somatomotor network in dystonia has an increased correlation with the medial prefrontal cortex and the paracingulate gyrus. Conclusions: These data suggest that unbalanced activation of the cerebellum, somatosensory, and frontal cortical areas are associated with dystonia. To our knowledge, this is the first study using fNIRS to explore the pathophysiology of dystonia. We show that fNIRS and fMRI are complementary methods and highlight the potential of fNIRS for the study of dystonia and other movement disorders as it can overcome movement restrictions, enabling experiments in more naturalistic conditions.

Background: Dystonia is known as a network disorder. There is evidence of volumetric changes in structures associated with the traditional physiopathology, such as basal nuclei. One approach to studying the neural pathways is through tractography, which can provide insights into the structural connectivity of neural networks that may be disrupted in dystonia. Objectives: To evaluate brain structural changes of motor networks and basal ganglia volume in dystonia. Methods: Twenty-six patients with right upper limb dystonia and 29 healthy controls underwent 3T magnetic resonance imaging and evaluated in terms of DTI and T1 data. The XTRACT FSL tool was utilized to examine fractional anisotropy of the bilateral anterior thalamic radiation, superior thalamic radiation, superior longitudinal fasciculus, cortical spinal tract, middle cerebellar peduncle, forceps major and forceps minor. Using T1-weithed data, volunteers were also evaluated in terms of volumetric changes in bilateral Putamen, Caudate, Pallidum and Thalamus extracted using Freesurfer 7.0 volumetric segmentation. For group comparison, we conducted an analysis of covariance controlling for sex and estimated intracranial volume. Results: For uncorrected p-values, patients with upper limb dystonia show diminished FA volume in the right corticospinal tract relative to controls (P = 0.025). Region of interest analysis of subcortical regions volume based on T1-weighted images shows that patients had diminished left caudate volume (P = 0.031) and right putamen (P = 0.041). However, using FDR multiple comparisons correction, no difference was observed between groups: right corticospinal tract (P = 0.329), left caudate volume (P = 0.16), right putamen volume (P = 0.16). Conclusion: Our study could not replicate previous findings describing structural changes in dystonia. This could be to methodological differences, as well as the fact that we selected only patients with upper limb dystonia, as opposed to studies that included other types of dystonia. The neuroimaging analyses were conducted with the utmost rigor, utilizing the optimal preprocessing and statistical analysis methods. The nature and characteristics of structural alterations remain unclear and may vary depending on the subtype of dystonia. Therefore, additional structural studies and meta-analyses are warranted to advance our knowledge of this network disorder.

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