Transcranial alternating current stimulation (tACS) mechanisms and protocols

Abstract

What if you could affect both neuroplasticity and human cognitive performance by parametrically modulating neural oscillations? Ongoing neuronal activity is susceptible to the modulation of synaptic activity and membrane potentials. This susceptibility leverages transcranial alternating current stimulation (tACS) for neuroplastic interventions. Through neuromodulation of phasic, neural activity, tACS presents a powerful tool for investigations of the neural correlates of cognition alongside other forms of transcranial electric stimulation (tES) and noninvasive brain stimulation (NIBS). The rapid pace of development in this area requires clarification of best practices. Here, we briefly introduce tACS dogma and review the most compelling findings from the tACS literature to provide a starting point for the use of tACS under research conditions.

Experience-dependent resonance in amygdalo-cortical circuits supports fear memory retrieval following extinction

“…frequency) of activation imposed on all projection neurons within a brain region. The latter type of manipulation might be easier to adapt for use in human subjects, as the critical parameter (frequency) can be tuned non-invasively using transcranial stimulation approaches 63 . Such strategies aimed at facilitating oscillatory resonance between brain regions have recently been shown to augment working memory in older patients 31 .…”

Transcranial electrical stimulation (tES) mechanisms and its effects on cortical excitability and connectivity

“…Polarisation of neurons reflects the current applied to it, leading to a sinusoidal fluctuation of the membrane potential. As this fluctuation is both frequency dependent and linearly proportional to the applied current, lower-frequency stimulation induces larger polarisation than does higher frequencies (Reato et al 2010 ) [see Tavakoli and Yun ( 2017 ) for a full description of tACS]. The ability to entrain neurons in a specific brain region to fire at a predetermined frequency enables researchers to identify the key frequencies involved in different behaviours and to draw causal links between them (Fig.…”

Beyond Hypnograms: Assessing Sleep Stability Using Acoustic and Electrical Stimulation

“…), the above reported spectral changes are likely to be the result of tACS. Although there are several controversies related to the mechanism of tACS action on brain, the most accepted mechanism is “direct entrainment of endogenous oscillators” by the “external electric field” . Therefore, as sleep is supposed to be resilient to external stimulations, spectral perturbations following tACS could imply a poorer sleep.…”

“…The effectiveness of tACS stimulations is modulated by many parameters that include frequency, amplitude, duration and shape of waveform, size and montage configuration of stimulating electrodes and phase of endogenous rhythm. Future studies can examine the effects of varying these parameters and assessing corresponding effects on the sleeping brain.…”