Cerebellar Transcranial Direct Current Stimulation in People with Parkinson’s Disease: A Pilot Study

Abstract

People with Parkinson’s disease (PwPD) often experience gait and balance problems that substantially impact their quality of life. Pharmacological, surgical, and rehabilitative treatments have limited effectiveness and many PwPD continue to experience gait and balance impairment. Transcranial direct current stimulation (tDCS) may represent a viable therapeutic adjunct. The effects of lower intensity tDCS (2 mA) over frontal brain areas, in unilateral and bilateral montages, has previously been explored; however, the effects of lower and higher intensity cerebellar tDCS (2 mA and 4 mA, respectively) on gait and balance has not been investigated. Seven PwPD underwent five cerebellar tDCS conditions (sham, unilateral 2 mA, bilateral 2 mA, unilateral 4 mA, and bilateral 4 mA) for 20 min. After a 10 min rest, gait and balance were tested. The results indicated that the bilateral 4 mA cerebellar tDCS condition had a significantly higher Berg Balance Scale score compared to sham. This study provides preliminary evidence that a single session of tDCS over the cerebellum, using a bilateral configuration at a higher intensity (4 mA), significantly improved balance performance. This intensity and cerebellar configuration warrants future investigation in larger samples and over repeated sessions.

Transcranial Direct Current Stimulation at 4 mA Induces Greater Leg Muscle Fatigability in Women Compared to Men

“…Interestingly, there was a trend toward significant stimulation condition differences in the 4 mA condition compared to sham (p = 0.069) in women, while there were no other differences observed in women or in men. This lack of significance might be due to the small number of participants (n = 10 in each group), but it may also strengthen the argument that higher intensities, e.g., ≥ 4 mA as suggested by Vöröslakos et al [4], might be required for sufficient current to reach the brain [4,15,22,45]. Vöröslakos et al [4] showed that only a small fraction of the transcranial current might reach the brain and up to 75% might be lost at the scalp, subcutaneous tissue, muscle, and skull.…”

“…Maintaining participant blinding integrity in repeated-session tDCS studies (when participants experience multiple tDCS conditions) is a constant limitation for repeated-measure study designs [64], and challenges with blinding might be greater at higher intensities (>2 mA). Sensation blinding might also be assessed by determining sensations experienced at different times during the stimulation period [45] or by changing the 'target' stimulation in the sham condition to match or exceed the highest used intensity. In this study, a common sham stimulation paradigm was used, but alternate methods, such as those described above [58], might improve blinding effectiveness.…”

Tolerability and Blinding of Transcranial Direct Current Stimulation in People with Parkinson’s Disease: A Critical Review

“…Study subjects had mild to moderate PD (Hoehn and Yahr (H&Y) range = 1.6–2.5). Two studies tested patients off dopaminergic medication [ 26 , 30 ] and three did not report medication status [ 24 , 27 , 32 ]. The study designs were heterogeneous: two studies were open-label (no subject or researcher blinding) [ 28 , 29 ]; three were parallel arm, randomized, double-blind, sham-controlled designs [ 25 , 27 , 32 ]; and four were crossover, randomized, sham-controlled designs, with two being double-blind [ 24 , 26 ], one being single-blind (subject) [ 31 ], and one with unstated blinding [ 30 ].…”

Different Effects of 2 mA and 4 mA Transcranial Direct Current Stimulation on Muscle Activity and Torque in a Maximal Isokinetic Fatigue Task

“…Future investigations should also include clinical populations with reduced cortical activity/excitability that might experience greater benefits from higher intensity tDCS (e.g., multiple sclerosis, stroke). Indeed, a preliminary 4 mA tDCS investigation in Parkinson’s disease indicated promising effects (Workman et al, 2020a ). This study also adds to the growing evidence that the performance effects of tDCS are highly variable.…”