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Transcranial magnetic stimulation coupled with electroencephalography (TMS-EEG) is a novel technique to investigate cortical physiology in health and disease. The cerebellum has recently gained attention as a possible new hotspot in the field of TMS-EEG, with several reports published recently. However, EEG responses obtained by cerebellar stimulation vary considerably across the literature, possibly due to different experimental methods. Compared to conventional TMS-EEG, which involves stimulation of the cortex, cerebellar TMS-EEG presents some technical difficulties, including strong muscle twitches in the neck area and a loud TMS click when double-cone coils are used, resulting in contamination of responses by electromyographic activity and sensory potentials. Understanding technical difficulties and limitations is essential for the development of cerebellar TMS-EEG research. In this review, we summarize findings of cerebellar TMS-EEG studies, highlighting limitations in experimental design and potential issues that can result in discrepancies between experimental outcomes. Lastly, we propose a possible direction for academic and clinical research with cerebellar TMS-EEG. [ABSTRACT FROM AUTHOR]

Transcranial magnetic stimulation coupled with electroencephalography (TMS-EEG) allows for the study of brain dynamics in health and disease. Cranial muscle activation can decrease the interpretability of TMS-EEG signals by masking genuine EEG responses and increasing the reliance on preprocessing methods but can be at least partly prevented by coil rotation coupled with the online monitoring of signals; however, the extent to which changing coil rotation may affect TMS-EEG signals is not fully understood. Our objective was to compare TMS-EEG data obtained with an optimal coil rotation to induce motor evoked potentials (M1standard) while rotating the coil to minimize cranial muscle activation (M1emg). TMS-evoked potentials (TEPs), TMS-related spectral perturbation (TRSP), and intertrial phase clustering (ITPC) were calculated in both conditions using two different preprocessing pipelines based on independent component analysis (ICA) or signal-space projection with source-informed reconstruction (SSP-SIR). Comparisons were performed with cluster-based correction. The concordance correlation coefficient was computed to measure the similarity between M1standard and M1emg TMS-EEG signals. TEPs, TRSP, and ITPC were significantly larger in M1standard than in M1emg conditions; a lower CCC than expected was also found. These results were similar across the preprocessing pipelines. While rotating the coil may be advantageous to reduce cranial muscle activation, it may result in changes in TMS-EEG signals; therefore, this solution should be tailored to the specific experimental context. [ABSTRACT FROM AUTHOR]

Cortical myoclonus is produced by abnormal neuronal discharges within the sensorimotor cortex, as demonstrated by electrophysiology. Our hypothesis is that the loss of cerebellar inhibitory control over the motor cortex, via cerebello-thalamo-cortical connections, could induce the increased sensorimotor cortical excitability that eventually causes cortical myoclonus. To explore this hypothesis, in the present study we applied anodal transcranial direct current stimulation over the cerebellum of patients affected by cortical myoclonus and healthy controls and assessed its effect on sensorimotor cortex excitability. We expected that anodal cerebellar transcranial direct current stimulation would increase the inhibitory cerebellar drive to the motor cortex and therefore reduce the sensorimotor cortex hyperexcitability observed in cortical myoclonus. Ten patients affected by cortical myoclonus of various aetiology and 10 aged-matched healthy control subjects were included in the study. All participants underwent somatosensory evoked potentials, long-latency reflexes and short-interval intracortical inhibition recording at baseline and immediately after 20 min session of cerebellar anodal transcranial direct current stimulation. In patients, myoclonus was recorded by the means of surface EMG before and after the cerebellar stimulation. Anodal cerebellar transcranial direct current stimulation did not change the above variables in healthy controls, while it significantly increased the amplitude of somatosensory evoked potential cortical components, long-latency reflexes and decreased short-interval intracortical inhibition in patients; alongside, a trend towards worsening of the myoclonus after the cerebellar stimulation was observed. Interestingly, when dividing patients in those with and without giant somatosensory evoked potentials, the increment of the somatosensory evoked potential cortical components was observed mainly in those with giant potentials. Our data showed that anodal cerebellar transcranial direct current stimulation facilitates—and does not inhibit—sensorimotor cortex excitability in cortical myoclonus syndromes. This paradoxical response might be due to an abnormal homeostatic plasticity within the sensorimotor cortex, driven by dysfunctional cerebello-thalamo-cortical input to the motor cortex. We suggest that the cerebellum is implicated in the pathophysiology of cortical myoclonus and that these results could open the way to new forms of treatment or treatment targets. [ABSTRACT FROM AUTHOR]

Background Objective Methods Results Conclusions Essential tremor (ET) is a common debilitating condition, yet current treatments often fail to provide satisfactory relief. Transcutaneous spinal cord electrical stimulation (tSCS) has emerged as a potential noninvasive neuromodulation technique capable of disrupting the oscillatory activity underlying tremors.This study aimed to investigate the potential of tSCS to disrupt tremor in a frequency‐dependent manner in a cohort of patients with ET.Eighteen patients with ET completed the study. The experiment consisted of 60‐s postural tremor recording, during tSCS at tremor frequency, at 1 Hz, at 21 Hz, no stimulation, and trapezius stimulation. Tremor frequency and amplitude were analyzed and compared across the conditions.We found tremor amplitude reduction at tremor frequency stimulation significant only during the second half of the stimulation. The same stimulation resulted in the highest number of responders. tSCS at 1 Hz showed a trend toward decreased tremor amplitude in the latter half of stimulation. tSCS at 21 Hz did not produce any significant alterations in tremor, whereas trapezius stimulation exacerbated it. Notably, during tremor frequency stimulation, a subgroup of responders exhibited consistent synchronization between tremor phase and delivered stimulation, indicating tremor entrainment.Cervical tSCS holds promise for alleviating postural tremor in patients with ET when delivered at the subject's tremor frequency. The observed changes in tremor amplitude likely result from the modulation of spinal cord circuits by tSCS, which disrupts the oscillatory drive to muscles by affecting afferent pathways or spinal reflexes. However, the possibility of an interplay between spinal and supraspinal centers cannot be discounted. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society. [ABSTRACT FROM AUTHOR]

Cortical myoclonus is produced by abnormal neuronal discharges within the sensorimotor cortex, as demonstrated by electrophysiology. Our hypothesis is that the loss of cerebellar inhibitory control over the motor cortex, via cerebello-thalamo-cortical connections, could induce the increased sensorimotor cortical excitability that eventually causes cortical myoclonus. To explore this hypothesis, in the present study we applied anodal transcranial direct current stimulation over the cerebellum of patients affected by cortical myoclonus and healthy controls and assessed its effect on sensorimotor cortex excitability. We expected that anodal cerebellar transcranial direct current stimulation would increase the inhibitory cerebellar drive to the motor cortex and therefore reduce the sensorimotor cortex hyperexcitability observed in cortical myoclonus. Ten patients affected by cortical myoclonus of various aetiology and 10 aged-matched healthy control subjects were included in the study. All participants underwent somatosensory evoked potentials, long-latency reflexes and short-interval intracortical inhibition recording at baseline and immediately after 20 min session of cerebellar anodal transcranial direct current stimulation. In patients, myoclonus was recorded by the means of surface EMG before and after the cerebellar stimulation. Anodal cerebellar transcranial direct current stimulation did not change the above variables in healthy controls, while it significantly increased the amplitude of somatosensory evoked potential cortical components, long-latency reflexes and decreased short-interval intracortical inhibition in patients; alongside, a trend towards worsening of the myoclonus after the cerebellar stimulation was observed. Interestingly, when dividing patients in those with and without giant somatosensory evoked potentials, the increment of the somatosensory evoked potential cortical components was observed mainly in those with giant potentials. Our data showed that anodal cerebellar transcranial direct current stimulation facilitates-and does not inhibit-sensorimotor cortex excitability in cortical myoclonus syndromes. This paradoxical response might be due to an abnormal homeostatic plasticity within the sensorimotor cortex, driven by dysfunctional cerebello-thalamo-cortical input to the motor cortex. We suggest that the cerebellum is implicated in the pathophysiology of cortical myoclonus and that these results could open the way to new forms of treatment or treatment targets., (© The Author(s) 2023. Published by Oxford University Press on behalf of the Guarantors of Brain.)