Cerebellar Transcranial Direct Current Stimulation (ctDCS): A Novel Approach to Understanding Cerebellar Function in Health and Disease

Transcranial direct current stimulation in treatment-resistant obsessive-compulsive disorder: An open-label pilot study

BACKGROUND

Obsessive-compulsive disorder (OCD) is a severe mental illness. OCD symptoms are often resistant to available treatments. Abnormalities within the orbitofronto-striato-pallido-thalamic circuitry, especially orbitofrontal cortex (OFC) hyperactivity and cerebellar hypoactivity have been observed in patients. Non-invasive brain stimulation studies have indicated that transcranial direct current stimulation (tDCS) may be a useful alternative to alleviate treatment-resistant symptoms in various neuropsychiatric conditions.

METHODS

In an open-label pilot study, 8 patients with treatment-resistant OCD received 10 sessions (twice a day) of 2mA tDCS applied with the cathode over the left OFC and the anode over the right cerebellum. OCD (Y-BOCS and OCD-VAS) as well as depressive (MADRS) symptoms were measured 4 times: one time before tDCS and 3 times after (immediately after, 1 and 3months after the 10th tDCS session).

RESULTS

We reported a significant 26.4% (±15.8) decrease of Y-BOCS score (p=0.002). The beneficial effect lasted during the 3month follow-up. No effect of tDCS was observed on depressive symptoms. At end point, 5 out of 8 patients had a decrease of ≥25%; and 3 out of 8 patients had a decrease of ≥35% in Y-BOCS score. tDCS was well tolerated.

CONCLUSION

tDCS with the cathode placed over the left OFC combined with the anode placed over the right cerebellum is a suitable and safe approach to decrease OCD symptoms in patients with treatment-resistant OCD. Large scale randomized controlled studies are needed to confirm this promising result.

A technical guide to tDCS, and related non-invasive brain stimulation tools

Transcranial electrical stimulation (tES), including transcranial direct and alternating current stimulation (tDCS, tACS) are non-invasive brain stimulation techniques increasingly used for modulation of central nervous system excitability in humans. Here we address methodological issues required for tES application. This review covers technical aspects of tES, as well as applications like exploration of brain physiology, modelling approaches, tES in cognitive neurosciences, and interventional approaches. It aims to help the reader to appropriately design and conduct studies involving these brain stimulation techniques, understand limitations and avoid shortcomings, which might hamper the scientific rigor and potential applications in the clinical domain.

Cerebellar direct current stimulation enhances on-line motor skill acquisition through an effect on accuracy

The cerebellum is involved in the update of motor commands during error-dependent learning. Transcranial direct current stimulation (tDCS), a form of noninvasive brain stimulation, has been shown to increase cerebellar excitability and improve learning in motor adaptation tasks. Although cerebellar involvement has been clearly demonstrated in adaptation paradigms, a type of task that heavily relies on error-dependent motor learning mechanisms, its role during motor skill learning, a behavior that likely involves error-dependent as well as reinforcement and strategic mechanisms, is not completely understood. Here, in humans, we delivered cerebellar tDCS to modulate its activity during novel motor skill training over the course of 3 d and assessed gains during training (on-line effects), between days (off-line effects), and overall improvement. We found that excitatory anodal tDCS applied over the cerebellum increased skill learning relative to sham and cathodal tDCS specifically by increasing on-line rather than off-line learning. Moreover, the larger skill improvement in the anodal group was predominantly mediated by reductions in error rate rather than changes in movement time. These results have important implications for using cerebellar tDCS as an intervention to speed up motor skill acquisition and to improve motor skill accuracy, as well as to further our understanding of cerebellar function.

Schmahmann's syndrome - identification of the third cornerstone of clinical ataxiology

Schmahmann’s syndrome represents a novel clinical condition consisting of a constellation of cognitive and affective deficits following cerebellar disease. The complex was first described in 1998 as cerebellar cognitive affective syndrome (CCAS) on the basis of a careful neurological examination, detailed bedside mental state tests, neuropsychological investigations and anatomical neuroimaging of a group of 20 patients with focal cerebellar disorders. The syndrome was characterized by four clusters of symptoms including: (a) impairment of executive functions such as planning, set-shifting, verbal fluency, abstract reasoning and working memory, (b) impaired visuo-spatial cognition, (c) personality changes with blunting of affect or abnormal behaviour, and (d) language deficits including agrammatism, wordfinding disturbances, disruption of language dynamics and dysprosodia. This complex of neurocognitive and behavioural-affective symptoms was ascribed to a functional disruption of the reciprocal pathways that connect the cerebellum with the limbic circuitry and the prefrontal, temporal and parietal association cortices. With the introduction of Schmahmann’s syndrome, clinical ataxiology has found its third cornerstone, the two others being the cerebellar motor syndrome (CMS) mainly delineated by the pioneer French and English neurologists of the 19^th and early 20^th century, and the vestibulo-cerebellar syndrome (VCS) consisting of ocular instability, deficits of oculomotor movements and ocular misalignment.