Cerebellar tDCS as Therapy for Cerebellar Ataxias

The "Cocombola Study": A Physical Phantom Model for tDCS-Induced Electric Field Distribution

BACKGROUND

Transcranial direct current stimulation (tDCS)-induced electric fields (EFs) acting on brain tissues are hardly controllable. Among physical models used in neuroscience research, watermelons are known as head-like phantoms for their dielectric properties. In this study, we aimed to define an inexpensive and reliable method to qualitatively define the spatial distribution of tDCS-induced EFs based on the use of watermelons.

METHODS

After creating the eight cranial foramina and identifying the location of the 21 EEG scalp electrodes on the peel of a watermelon, voltage differences during stimulation were recorded in each of the 21 scalp electrode positions, one at a time, at four different depths. The recordings were graphically represented by using polar coordinates with the watermelon approximated to a perfect sphere.

RESULTS

To validate the model, we performed three experiments in well-known montages. The results obtained were in line with the expected behavior of the EFs.

CONCLUSIONS

Watermelon might be a cheap and feasible phantom head model to characterize the EFs induced by tDCS and, potentially, even other non-invasive brain stimulation techniques.

Cerebellar Transcranial Direct Current Stimulation in the Cerebellar Cognitive Affective Syndrome: A Randomized, Double-Blind, Sham-Controlled Trial

BACKGROUND

The cerebellar cognitive affective syndrome (CCAS) encompasses cognitive and affective symptoms in patients with cerebellar disorders, for which no proven treatment is available.

OBJECTIVES

Our primary objective was to study the effect of cerebellar anodal transcranial direct current stimulation (tDCS) on cognitive performance in CCAS patients. Secondary effects on ataxia severity, mood, and quality of life were explored.

METHODS

We performed a randomized, double-blind, sham-controlled trial. Thirty-five patients with CCAS were included and received 10 sessions of 20 minutes sham (n = 17) or real (n = 18) tDCS, with a current of 2 mA. Cognitive performance was assessed using executive function subtests of the computerized Test of Attentional Performance (TAP), with the composite as primary endpoint. Secondary outcomes were ataxia severity, mood, and quality of life. Outcomes were evaluated 1, 3, 6, and 12 months post-intervention.

RESULTS

Cerebellar tDCS was well tolerated and no serious adverse events related to the intervention occurred. No significant tDCS effect was found on cognitive performance. Improvement on the TAP was observed in the sham group 1 month post-treatment (estimate = -0.248, 95% CI, -0.49 to -0.01), but not clinically relevant. A positive tDCS effect was observed for ataxia severity 1 month post-treatment (estimate = -0.985, 95% CI, -1.94 to -0.03).

CONCLUSIONS

Ten sessions of 20 minutes cerebellar anodal tDCS did not prove efficacious for CCAS-related cognitive impairment, but a significant positive effect of tDCS was found for ataxia severity, aligning with previous findings indicative of tDCS as a therapeutic neuromodulation tool in cerebellar disorders. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Transcranial direct current stimulation targeting the bilateral IFG alters cognitive processes during creative ideation

This study investigated whether transcranial direct current stimulation (tDCS) targeting the inferior frontal gyrus (IFG) can alter the thinking process and neural basis of creativity. Participants' performance on the compound remote associates (CRA) task was analyzed considering the semantic features of each trial after receiving different tDCS protocols (left cathodal and right anodal, L + R-; right cathodal and left anodal, L-R+; and Sham). Moreover, we constructed and compared 80 prediction models of CRA performance for each group based on task-related functional connectivity. Results showed that L + R- stimulation improved performance in semantically bundled CRA trials, while L-R+ stimulation enhanced performance in trials with greater semantic distance. Furthermore, alpha-band task connectivity models for the L + R- group showed inferior performance and greater left frontal lateralization than other two groups. These findings suggest that tDCS targeting the bilateral IFG alters cognitive processes during creative ideation rather than enhancing or impairing an established thinking process.

Quantification of Solid Embryonic Cerebellar Graft Volume in a Degenerative Ataxia Model

Substitution of lost neurons by neurotransplantation would be a possible management of advanced degenerative cerebellar ataxias in which insufficient cerebellar reserve remains. In this study, we examined the volume and structure of solid embryonic cerebellar grafts in adult Lurcher mice, a model of olivocerebellar degeneration, and their healthy littermates. Grafts taken from enhanced green fluorescent protein (EGFP)-positive embryos were injected into the cerebellum of host mice. Two or six months later, the brains were examined histologically. The grafts were identified according to the EGFP fluorescence in frozen sections and their volumes were estimated using the Cavalieri principle. For gross histological evaluation, graft-containing slices were processed using Nissl and hematoxylin-eosin staining. Adjustment of the volume estimation approach suggested that it is reasonable to use all sections without sampling, but that calculation of values for up to 20% of lost section using linear interpolation does not constitute substantial error. Mean graft volume was smaller in Lurchers than in healthy mice when examined 6 months after the transplantation. We observed almost no signs of graft destruction. In some cases, compact grafts disorganized the structure of the host's cerebellar cortex. In Lurchers, the grafts had a limited contact with the host's cerebellum. Also, graft size was of greater variability in Lurchers than in healthy mice. The results are in compliance with our previous findings that Lurcher phenotype-associated factors have a negative effect on graft development. These factors can hypothetically include cerebellar morphology, local tissue milieu, or systemic factors such as immune system abnormalities.

Clinical neurophysiology in the treatment of movement disorders: IFCN handbook chapter

In this review, different aspects of the use of clinical neurophysiology techniques for the treatment of movement disorders are addressed. First of all, these techniques can be used to guide neuromodulation techniques or to perform therapeutic neuromodulation as such. Neuromodulation includes invasive techniques based on the surgical implantation of electrodes and a pulse generator, such as deep brain stimulation (DBS) or spinal cord stimulation (SCS) on the one hand, and non-invasive techniques aimed at modulating or even lesioning neural structures by transcranial application. Movement disorders are one of the main areas of indication for the various neuromodulation techniques. This review focuses on the following techniques: DBS, repetitive transcranial magnetic stimulation (rTMS), low-intensity transcranial electrical stimulation, including transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS), and focused ultrasound (FUS), including high-intensity magnetic resonance-guided FUS (MRgFUS), and pulsed mode low-intensity transcranial FUS stimulation (TUS). The main clinical conditions in which neuromodulation has proven its efficacy are Parkinson's disease, dystonia, and essential tremor, mainly using DBS or MRgFUS. There is also some evidence for Tourette syndrome (DBS), Huntington's disease (DBS), cerebellar ataxia (tDCS), and axial signs (SCS) and depression (rTMS) in PD. The development of non-invasive transcranial neuromodulation techniques is limited by the short-term clinical impact of these techniques, especially rTMS, in the context of very chronic diseases. However, at-home use (tDCS) or current advances in the design of closed-loop stimulation (tACS) may open new perspectives for the application of these techniques in patients, favored by their easier use and lower rate of adverse effects compared to invasive or lesioning methods. Finally, this review summarizes the evidence for keeping the use of electromyography to optimize the identification of muscles to be treated with botulinum toxin injection, which is indicated and widely performed for the treatment of various movement disorders.

Advances in cerebellar disorders: pre-clinical models, therapeutic targets, and challenges

INTRODUCTION

Cerebellar ataxias (CAs) represent neurological disorders with multiple etiologies and a high phenotypic variability. Despite progress in the understanding of pathogenesis, few therapies are available so far. Closing the loop between preclinical studies and therapeutic trials is important, given the impact of CAs upon patients' health and the roles of the cerebellum in multiple domains. Because of a rapid advance in research on CAs, it is necessary to summarize the main findings and discuss future directions.

AREAS COVERED

We focus our discussion on preclinical models, cerebellar reserve, the therapeutic management of CAs, and suitable surrogate markers. We searched Web of Science and PubMed using keywords relevant to cerebellar diseases, therapy, and preclinical models.

EXPERT OPINION

There are many symptomatic and/or disease-modifying therapeutic approaches under investigation. For therapy development, preclinical studies, standardization of disease evaluation, safety assessment, and demonstration of clinical improvements are essential. Stage of the disease and the level of the cerebellar reserve determine the goals of the therapy. Deficits in multiple categories and heterogeneity of CAs may require disease-, stage-, and symptom-specific therapies. More research is needed to clarify how therapies targeting the cerebellum influence both basal ganglia and the cerebral cortex, poorly explored domains in CAs.

Low-Intensity Transcranial Ultrasound Stimulation: Mechanisms of Action and Rationale for Future Applications in Movement Disorders

Low-intensity transcranial ultrasound stimulation (TUS) is a novel non-invasive brain stimulation technique that uses acoustic energy to induce changes in neuronal activity. However, although low-intensity TUS is a promising neuromodulation tool, it has been poorly studied as compared to other methods, i.e., transcranial magnetic and electrical stimulation. In this article, we first focus on experimental studies in animals and humans aimed at explaining its mechanisms of action. We then highlight possible applications of TUS in movement disorders, particularly in patients with parkinsonism, dystonia, and tremor. Finally, we highlight the knowledge gaps and possible limitations that currently limit potential TUS applications in movement disorders. Clarifying the potential role of TUS in movement disorders may further promote studies with therapeutic perspectives in this field.