Non-Invasive Cerebellar Stimulation in Neurodegenerative Ataxia: A Literature Review

Abstract

Cerebellar ataxias are a heterogenous group of degenerative disorders for which we currently lack effective and disease-modifying interventions. The field of non-invasive brain stimulation has made much progress in the development of specific stimulation protocols to modulate cerebellar excitability and try to restore the physiological activity of the cerebellum in patients with ataxia. In light of limited evidence-based pharmacologic and non-pharmacologic treatment options for patients with ataxia, several different non-invasive brain stimulation protocols have emerged, particularly employing repetitive transcranial magnetic stimulation (rTMS) or transcranial direct current stimulation (tDCS) techniques. In this review, we summarize the most relevant rTMS and tDCS therapeutic trials and discuss their implications in the care of patients with degenerative ataxias.

Individual Cerebral Blood Flow Responses to Transcranial Direct Current Stimulation at Various Intensities

“…Similarly, these results support the high variability evident in several reviews and meta-analyses [ 8 , 9 , 10 , 11 , 12 , 13 ] and continue to raise questions regarding the ability of sufficient residual current to reach the cortex and reliably affect brain function. Indeed, an animal and cadaver study concluded that higher intensities (≥4 mA) might be required to adequately overcome skin/skull electrical current shunting [ 17 ].…”

“…This neuromodulation technique has several desirable characteristics, including ease of use, low cost, and potential for in-home use [ 7 ]. However, as more results from tDCS studies continue to be published, it is becoming increasingly evident that this neuromodulatory tool is hampered by high inter- and intra-subject variability [ 8 , 9 , 10 ]. Indeed, the results of some meta-analyses challenge the efficacy of tDCS [ 11 , 12 , 13 ], although a group of tDCS experts has argued against some of these null meta-findings [ 14 ].…”

Response Variability in Transcranial Direct Current Stimulation: Why Sex Matters

“…This neglect may account for some of the high inter-subject variability bemoaned by many tDCS investigators and has certainly delayed progress in the field. This is unfortunate because research into sex influences is vital to fully understanding the underlying mechanisms of non-invasive brain stimulation, especially for tDCS which has shown great variability (7)(8)(9)(10)(11)(12)(13). Indeed, approximately 50% of participants do not respond to tDCS and some even show effects contrary to the expected excitability response (e.g., inhibition from anodal tDCS and excitation from cathodal tDCS), evidenced by amplitude changes in motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) (14-16).…”

Neuromodulation in the Age of Modern Neuroimaging Technologies

“…Transcranial direct current stimulation (tDCS) is another form of noninvasive brain stimulation techniques that is easily available and not extensive, while the exact mechanism of action has not been yet discovered [63,64]. In this method, electrodes are placed on the scalp and they conduct weak prolonged (about 10-20 min) currents to brain tissues.…”