Effects of Cerebellar Transcranial Alternating Current Stimulation on Gait and Balance in Healthy Subjects

Abstract

Transcranial Alternating Current Stimulation (tACS) is a non-invasive brain stimulation technique [1] able to modulate neural oscillatory activities, including those linked to the cortico-cerebello-thalamo- cortical network [2,3]. In this double-blind sham-controlled study, we aimed to investigate the effects of cerebellar tACS delivered at theta and gamma frequencies on gait and balance in healthy subjects, as assessed by kinematic techniques. In a group of young healthy subjects, we applied tACS over the dominant cerebellar hemisphere during the execution of three different motor tasks: 1) standing (both with eyes open and closed); 2) gait initiation (assessed both for the dominant and non-dominant lower limb); 3) 5-meter walk test (5MWT) (Fig. 1). tACS was delivered in a random order at the theta (5 Hz, theta-tACS) and gamma (50 Hz, gamma-tACS) frequencies, and sham-tACS was used as a control condition. The stimulation intensity was set at 1,5 mA and the stimulation duration lasted as long as the motor task was accomplished. Kinematic data were obtained using a force platform and an optoelectronic system. The data analysis was conducted using a dedicated software. Theta-tACS induced a significant reduction of the Centre Of Pressure (COP) displacement during standing with eyes closed compared to sham- and gamma-tACS (mean radius displacement: theta- tACS 4.65±0.74 mm, gamma-tACS 5.58±1.26 mm, sham-tACS 5.99±2.12 mm). A similar, though weaker, trend was present in the eyes open condition. Furthermore, stride width during 5MWT resulted tighter during theta-tACS compared to sham- and gamma tACS. Boosting theta oscillations in the cerebellum through tACS improves balance during standing and gait in healthy subjects. This effect may rely on the modulation of the activity of cerebellar neurons resonant to the theta rhythm. This non-invasive neuromodulation approach could be applied in neurological conditions characterized by ataxia to possibly ameliorate the imbalance and reduce the risk of falling.