Evaluation of microstates and functional connectivity after transcranial direct current stimulation in post-covid syndrome

Abstract

INTRODUCTION: Post-covid syndrome (PCS) includes symptoms such as chronic fatigue, mood disorder, or cognitive impairment. Studies employing transcranial direct current stimulation (tDCS) in different diagnoses have found improvement of fatigue and cognition. AIM: tDCS intervention was performed in PCS patients, with subsequent analysis of certain EEG parameters – microstates (MS) and functional connectivity (FC). METHODS: A randomized two-arm sham-controlled trial, with 33 participants (16 in active, 17 in sham group), consisting of 20 tDCS sessions, lasting 30 min, with the intensity 2 mA, with electrodes placed at F3-F4 (anode-cathode) was performed. tDCS was performed at home. Resting-state EEG was recorded before tDCS, after 2 weeks, and after tDCS (4 weeks); MS and FC analysis was performed. For MS, duration, occurrence, topographic maps, and transitions were evaluated using Wilcoxon test, with Bonferroni correction for multiple comparisons. FC was calculated as mean of each 2-second window FC between the F3-F4 electrodes and analysed with two-sample t-test. RESULTS: Difference between active and sham group was tested for changes in time points: baseline/2-weeks and baseline/4-weeks. No significant difference was found, both for MS and FC [T = -0.57, p = 0.58 (after two weeks); T = -0.75, p = 0.46 (after four weeks)]. Most common adverse effects (AEs) were tingling and burning sensation. No serious AEs were reported. No significant change was also found in clinical parameters and cognition. CONCLUSION: tDCS in at-home setup is a safe method. The intervention with abovementioned parameters did not result in changes of MS or FC. Different electrode montage, intensity, or duration, and evaluation of different EEG parameters (such as power spectral density) might yield different results. Correlating clinical and EEG changes might help uncover the underlying pathology of PCS. Supported by ERDF-Project Brain Dynamics, No. CZ.02.01.01/00/22_008/0004643, grant No. 118724 of Charles University Grant Agency, Charles University research program Cooperatio-Neurosciences, and CNPS.