The effect of gamma oscillations in boosting primary motor cortex plasticity is greater in young than older adults

Objective: In healthy subjects, the long-term potentiation (LTP)-like plasticity of the primary motor cortex (M1) induced by intermittent theta-burst stimulation (iTBS) can be boosted by modulating gamma (gamma) oscillations through transcranial alternating current stimulation (tACS). gamma-tACS also reduces short-interval intracortical inhibition (SICI). We tested whether the effects of gamma-tACS differ between young (YA) and older adults (OA). Methods: Twenty YA (27.2 +/- 2.7 years) and twenty OA (65.3 +/- 9.5 years) underwent iTBS-gamma tACS and iTBS-sham tACS in randomized sessions. In a separate session, we delivered gamma-tACS alone and recorded SICI during stimulation. Results: iTBS-sham tACS produced comparable motor evoked potential (MEP) facilitation between groups. While iTBS-gamma tACS boosted MEP facilitation in both the YA and OA groups, the magnitude of its effect was significantly lower in OA. Similarly, gamma-tACS-induced modulation of GABA-A-ergic neuro-transmission, as tested by SICI, was reduced in OA. The effect of iTBS-gamma tACS negatively correlated with the age of OA subjects. Conclusions: Mechanisms underlying the effects of gamma oscillations on LTP-like plasticity become less efficient in older adults. This could reflect age-related changes in neural elements of M1 resonant to gamma oscillations, including GABA-A-ergic interneurons. Significance: The beneficial effect of gamma-tACS on iTBS-induced plasticity is reduced in older adults. (C) 2021 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.

Automated summary

The study showed that the effects of transcranial alternating current stimulation (tACS) on long-term potentiation (LTP)-like plasticity of the primary motor cortex (M1) are significantly reduced in older adults compared to young adults.