Effects of transcranial alternating current stimulation on repetitive finger movements in healthy humans

G Paparella,A Guerra,M Bologna,A Suppa,D Colella,V Di Lazzaro,P Brown,A Berardelli

doi:10.1016/j.clinph.2018.09.086

Abstract

Transcranial Alternating Current Stimulation (tACS) is a non-invasive technique that can entrain brain oscillations. Few studies have investigated the effects of tACS on voluntary movements in healthy humans. We investigated whether tACS, delivered over M1 at beta and gamma frequencies, has any effect on repetitive finger tapping as assessed by means of kinematic analysis. Eighteen healthy subjects were enrolled. Objective measurements of repetitive finger tapping were obtained by using a motion analysis system. M1 excitability was assessed by single pulse TMS and measuring the amplitude of motor-evoked potentials. Movement kinematics and M1 excitability measures were collected during beta, gamma and sham tACS as well as off stimulation. Beta tACS led to an early amplitude decrement during repetitive finger tapping. Gamma tACS had the opposite effect. The progressive but short-lived modulatory effect of beta and gamma tACS on amplitude decrement was marked during the first movements of the motor sequence. No effect of tACS were found on other movement parameters neither on MEP amplitude. tACS modulates finger tapping in a frequency-dependent manner with no concurrent changes in corticospinal excitability. Thus, cortical beta and gamma oscillations are involved in the motor control of repetitive finger movements.

Highlights

A growing number of studies on humans have shown that the two main natural rhythms of the primary motor cortex (M1), namely, beta (13–30 Hz) and gamma (30–100 Hz), play a role in motor control
We demonstrate that in healthy humans, beta Transcranial alternating current stimulation (tACS) leads to an early and progressive reduction in amplitude during repetitive finger tapping while gamma tACS has the opposite effect
As the tapping sequence continues still, further physiological fatigue sets in [23], but this is unaffected by tACS. tACS, as applied here, does not significantly affect other movement parameters, including overall movement amplitude, velocity, and rhythm which are mediated by distinct physiological mechanisms [26,27,28]

Summary

Introduction

A growing number of studies on humans have shown that the two main natural rhythms of the primary motor cortex (M1), namely, beta (13–30 Hz) and gamma (30–100 Hz), play a role in motor control. The contrasting functional effects of the two frequency bands of activity are supported by the effects of electrical stimulation on healthy subjects [10,11,12] and by the changes observed in patients with Parkinson’s disease (PD). In this condition, untreated patients have elevated beta activity in basal ganglia-cortical circuits and slowed movement [13], whereas dyskinetic treated patients have elevated gamma activity at about 70 Hz and have excessive movement [14, 15]. The resulting neuronal synchronization may affect the activity of different cortical areas in a frequency-specific manner, resulting in the so-called “resonance principle.” Namely, the ability of tACS to modify brain rhythms especially when the externally superimposed oscillation is close to the natural frequency of the cortical area is stimulated [17, 18]

Objectives

Methods

Results

Conclusion