Objective: To test whether the co-stimulation γ-transcranial alternating current stimulation (γ-tACS)-intermittent theta burst stimulation (iTBS) is effective in improving the impaired long-term potentiation (LTP)-like plasticity of the primary motor cortex (M1) in patients with Parkinson’s Disease (PD).

Background: Several transcranial magnetic stimulation studies have shown that iTBS fails to induce long-lasting changes in motor evoked potentials (MEPs) in PD, supporting the evidence of an impaired LTP-like plasticity in M1. We have recently introduced a novel neurophysiological approach consisting in the combined stimulation of M1 by tACS, delivered at the γ frequency, and iTBS, which produced a significant boosting of the LTP-like plasticity in healthy young subjects.

Method: We designed a single-blinded placebo-controlled study in which patients (‘OFF’ dopaminergic therapy) underwent iTBS during ‘real’ γ-tACS and during ‘sham’ γ-tACS in two different randomized sessions. MEPs were recorded from the most affected side before (T0) and after 5 (T1), 15 (T2) and 30 (T3) minutes after the intervention to measure the after-effects produced by the stimulation. A group of age- and sex-matched healthy subjects (HS) was also studied to compare the effect of γ-tACS-iTBS with that obtained in patients.

Results: In HS, ‘sham’ γ-tACS-iTBS produced a significant MEPs facilitation at T1 and T2. By contrast, the same stimulation did not induce long-lasting changes of MEPs in patients. When the effect of ‘real’ γ-tACS-iTBS was compared with that produced by ‘sham’ γ-tACS-iTBS, the analysis demonstrated an increased MEPs facilitation at all the time-points in the ‘real’ session in both groups. Importantly, in patients, the MEPs amplitude at T1, T2 and T3 was higher than those recorded at T0, and the amount of facilitation was comparable with that observed in HS. The effect produced by γ-tACS-iTBS was not related to the patient’s age, most affected side, stage of the disease or severity of the motor symptoms.

Conclusion: iTBS-induced LTP-like plasticity is impaired in PD. However, by synchronizing the neuronal elements of M1 at the γ rhythm by using tACS, the mechanisms responsible for altered LTP-like plasticity can be restored. Thus, γ oscillations of M1 have an important pathophysiological role in LTP-like plasticity in PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/impaired-ltp-like-plasticity-in-parkinsons-disease-can-be-restored-by-%ce%b3-transcranial-alternating-current-stimulation/