Combined transcranial alternating current stimulation and continuous theta burst stimulation: a novel approach for neuroplasticity induction

Abstract

Non‐invasive brain stimulation can induce functionally relevant plasticity in the human cortex, making it potentially useful as a therapeutic tool. However, the induced changes are highly variable between individuals, potentially limiting research and clinical utility. One factor that might contribute to this variability is the level of cortical inhibition at the time of stimulation. The alpha rhythm (~ 8–13 Hz) recorded with electroencephalography (EEG) is thought to reflect pulsatile cortical inhibition; therefore, targeting non‐invasive brain stimulation to particular phases of the alpha rhythm may provide an approach to enhance plasticity induction. Transcranial alternating current stimulation (tACS) has been shown to entrain cortical oscillations in a frequency‐specific manner. We investigated whether the neuroplastic response to continuous theta burst stimulation (cTBS) was enhanced by timing bursts of stimuli to the peak or the trough of a tACS‐imposed alpha rhythm. While motor evoked potentials (MEPs) were unaffected when cTBS was applied in‐phase with the peak of the tACS‐imposed oscillation, MEP depression was enhanced when cTBS was applied in‐phase with the trough. This enhanced MEP depression was dependent on the individual peak frequency of the endogenous alpha rhythm recorded with EEG prior to stimulation, and was strongest in those participants classified as non‐responders to standard cTBS. These findings suggest that tACS may be used in combination with cTBS to enhance the plasticity response. Furthermore, the peak frequency of endogenous alpha, as measured with EEG, may be used as a simple marker to pre‐select those individuals likely to benefit from this approach.

Guiding transcranial brain stimulation by EEG/MEG to interact with ongoing brain activity and associated functions: A position paper

“…Other combinations are conceivable, e.g., testing whether the pulses of plasticity inducing TMS protocols would be more effective if tuned to specific phases of simultaneously applied TACS, in particular when the latter is frequency-tuned to physiologically meaningful oscillations (see Goldsworthy et al, 2016). This is analogous to the idea that the efficacy of these protocols may be enhanced if TMS pulses are phase-locked in real-time to EEG-signals (see section 3.1 above).…”

Can genetic polymorphisms predict response variability to anodal transcranial direct current stimulation of the primary motor cortex?

“…'non-responders'). This dichotomy, termed inter-individual variability, extends to other NIBS protocols including Theta Burst Stimulation (TBS) (Goldsworthy et al, 2016;Hamada et al, 2013;Hinder et al, 2014;López-Alonso et al, 2014Nettekoven et al, 2015;Puri et al, 2016;Vallence et al, 2015) and Paired Associative Stimulation (Labruna et al, 2016;López-Alonso et al, 2014F. Müller-Dahlhaus et al, 2015;J.…”

Combining TMS and tACS for Closed-Loop Phase-Dependent Modulation of Corticospinal Excitability: A Feasibility Study

“…Moreover, to deliver TMS at the desired phase of the tACS, calibration of the systematic time-lag was applied, thereby addressing the precision problem. The basic concept of combining tACS with TMS has already been applied, e.g., to assess pre-post changes in cortical excitability following repetitive stimuli (Goldsworthy et al, 2016 ). It has also been used at a very low tACS frequency (0.8 Hz) with a positive current offset (Bergmann et al, 2009 ).…”