Abstract
A growing body of research suggests that non-invasive electrical brain stimulation can more effectively modulate neural activity when phase-locked to the underlying brain rhythms. Transcranial alternating current stimulation (tACS) can potentially stimulate the brain in-phase to its natural oscillations as recorded by electroencephalography (EEG), but matching these oscillations is a challenging problem due to the complex and time-varying nature of the EEG signals. Here we address this challenge by developing and testing a novel approach intended to deliver tACS phase-locked to the activity of the underlying brain region in real-time. This novel approach extracts phase and frequency from a segment of EEG, then forecasts the signal to control the stimulation. A careful tuning of the EEG segment length and prediction horizon is required and has been investigated here for different EEG frequency bands. The algorithm was tested on EEG data from 5 healthy volunteers. Algorithm performance was quantified in terms of phase-locking values across a variety of EEG frequency bands. Phase-locking performance was found to be consistent across individuals and recording locations. With current parameters, the algorithm performs best when tracking oscillations in the alpha band (8–13 Hz), with a phase-locking value of 0.77 ± 0.08. Performance was maximized when the frequency band of interest had a dominant frequency that was stable over time. The algorithm performs faster, and provides better phase-locked stimulation, compared to other recently published algorithms devised for this purpose. The algorithm is suitable for use in future studies of phase-locked tACS in preclinical and clinical applications.
Highlights
Transcranial electrical stimulation has shown considerable promise for modulating brain activity in both preclinical and clinical applications (Nitsche and Paulus, 2000; Kuo and Nitsche, 2012; Dayan et al, 2013; Ruffini et al, 2013; Karabanov et al, 2016)
EEG Forecasting for Brain Stimulation such as Transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation have the potential to become effective and inexpensive interventions for neurological and psychiatric illnesses characterized by abnormal brain activity
“Closed-loop” techniques, in which target brain activity via neurophysiological recording modalities like electroencephalography (EEG) is used as an input signal to continuously fine-tune the parameters of stimulation, are increasingly employed for invasive stimulatory therapies such as deep brain stimulation (DBS) (Rosin et al, 2011; Widge et al, 2017) or responsive neurostimulation (RNS) in the setting of epilepsy (Sun and Morrell, 2014)
Summary
Transcranial electrical stimulation (tES) has shown considerable promise for modulating brain activity in both preclinical and clinical applications (Nitsche and Paulus, 2000; Kuo and Nitsche, 2012; Dayan et al, 2013; Ruffini et al, 2013; Karabanov et al, 2016). Transcranial direct current stimulation (tDCS) is one tES modality with mounting evidence of efficacy as a treatment for an increasingly wide range of neurological or psychiatric disorders in recent studies and meta-analyses (Fregni et al, 2006, 2007; Nitsche et al, 2009; Brunoni et al, 2011; Brunelin et al, 2012; Kuo et al, 2014; Meron et al, 2015). Thanks to their safety, non-invasiveness, and low cost, tES techniques. Closed-loop techniques are far less commonly employed for non-invasive stimulation modalities such as tES, and few studies of such approaches exist in the current literature (for a recent review, see Karabanov et al, 2016)
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