Objective: To test whether driving beta (β) and gamma (γ) rhythms of the primary motor cortex (M1) by using transcranial alternating current stimulation (tACS) modulates voluntary movements abnormalities and M1 excitability in patients with Parkinson’s disease (PD).

Background: β and γ are the main resonant rhythms of M1 in humans. In patients with PD, β and γ oscillatory activities are altered within the basal ganglia, and this abnormality contributes to the pathophysiology of motor symptoms, including bradykinesia. However, whether cortical β and γ oscillations influence bradykinesia in PD is still unclear. tACS is a neurophysiological technique that entrains cortical rhythms, transiently increasing their power.

Method: Kinematic features of repetitive finger movement were recorded during β-, γ- and sham-tACS, delivered in a random order over M1. In the same stimulation conditions, we also recorded motor evoked potentials (MEPs) elicited by single and paired-pulse transcranial magnetic stimulation (short-interval intracortical inhibition – SICI, and short-latency afferent inhibition – SAI). Patients were studied OFF and ON therapy, in two different randomized sessions. A group of healthy subjects (HS) was also tested.

Results: Patients showed various movement abnormalities compared to HS. SICI was higher (reduced inhibition) in patients than in HS. In patients, β- tACS deteriorated movement amplitude and velocity, while γ-tACS slightly improved these parameters. Also, β-tACS decreased (reduced inhibition) both SICI and SAI, whereas γ- tACS decreased SICI. The effects of tACS were independent of the medication status (OFF or ON). In PD OFF state, during β-tACS, the degree of SICI correlated with movement velocity.

Conclusion: In PD, specific bradykinesia features and intracortical excitability measures of M1 are modulated by β- and γ-tACS. Our findings support the evidence for an anti-kinetic role of cortical β oscillations in PD, and suggest a relationship between the β-induced worsening of bradykinesia and GABA-A-ergic interneuronal activity, as tested by SICI.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/driving-motor-rhythms-modulates-bradykinesia-and-cortical-excitability-in-parkinsons-disease/