Boosting the LTP-like plasticity effect of intermittent theta-burst stimulation using gamma transcranial alternating current stimulation

• Published in: Brain stimulation Vol. 11; no. 4; pp. 734 - 742
• Main Authors: Guerra, Andrea, Suppa, Antonio, Bologna, Matteo, D'Onofrio, Valentina, Bianchini, Edoardo, Brown, Peter, Di Lazzaro, Vincenzo, Berardelli, Alfredo
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.07.2018
• Subjects: Adult; Evoked Potentials, Motor; Female; GABA-A; Gamma; Gamma Rhythm; Humans; Interneurons; Long-Term Potentiation; Male; Motor Cortex - physiology; Plasticity; tACS; Theta Rhythm; TMS; Transcranial Direct Current Stimulation - methods; Interneurons; M1; tACS; iTBS; Gamma; β; γ; GABA-A; tACST; Plasticity; RMT; SICI; TMS; TMST
• ISSN: 1935-861X; 1876-4754; 1876-4754
• DOI: 10.1016/j.brs.2018.03.015

Transcranial Alternating Current Stimulation (tACS) consists in delivering electric current to the brain using an oscillatory pattern that may entrain the rhythmic activity of cortical neurons. When delivered at gamma frequency, tACS modulates motor performance and GABA-A-ergic interneuron activity. Since interneuronal discharges play a crucial role in brain plasticity phenomena, here we co-stimulated the primary motor cortex (M1) in healthy subjects by means of tACS during intermittent theta-burst stimulation (iTBS), a transcranial magnetic stimulation paradigm known to induce long-term potentiation (LTP)-like plasticity. We measured and compared motor evoked potentials before and after gamma, beta and sham tACS-iTBS. While we delivered gamma-tACS, we also measured short-interval intracortical inhibition (SICI) to detect any changes in GABA-A-ergic neurotransmission. Gamma, but not beta and sham tACS, significantly boosted and prolonged the iTBS-induced after-effects. Interestingly, the extent of the gamma tACS-iTBS after-effects correlated directly with SICI changes. Overall, our findings point to a link between gamma oscillations, interneuronal GABA-A-ergic activity and LTP-like plasticity in the human M1. Gamma tACS-iTBS co-stimulation might represent a new strategy to enhance and prolong responses to plasticity-inducing protocols, thereby lending itself to future applications in the neurorehabilitation setting. •γ-tACS boosts and prolongs iTBS-induced LTP-like plasticity in human M1.•β-tACS leaves the iTBS-related LTP-like plasticity unchanged.•GABA-A inhibitory intracortical neurotransmission is reduced during γ-tACS on M1.•The effect of iTBS-γ tACS is directly related to γ tACS-induced modulation of SICI.