The Effects of 10 Hz and 20 Hz tACS in Network Integration and Segregation in Chronic Stroke: A Graph Theoretical fMRI Study

Abstract

Transcranial alternating current stimulation (tACS) has emerged as a promising technique to non-invasively modulate the endogenous oscillations in the human brain. Despite its clinical potential to be applied in routine rehabilitation therapies, the underlying modulation mechanism has not been thoroughly understood, especially for patients with neurological disorders, including stroke. In this study, we aimed to investigate the frequency-specific stimulation effect of tACS in chronic stroke. Thirteen chronic stroke patients underwent tACS intervention, while resting-state functional magnetic resonance imaging (fMRI) data were collected under various frequencies (sham, 10 Hz and 20 Hz). The graph theoretical analysis indicated that 20 Hz tACS might facilitate local segregation in motor-related regions and global integration at the whole-brain level. However, 10 Hz was only observed to increase the segregation from whole-brain level. Additionally, it is also observed that, for the network in motor-related regions, the nodal clustering characteristic was decreased after 10 Hz tACS, but increased after 20 Hz tACS . Taken together, our results suggested that tACS in various frequencies might induce heterogeneous modulation effects in lesioned brains. Specifically, 20 Hz tACS might induce more modulation effects, especially in motor-related regions, and they have the potential to be applied in rehabilitation therapies to facilitate neuromodulation. Our findings might shed light on the mechanism of neural responses to tACS and facilitate effectively designing stimulation protocols with tACS in stroke in the future.

Improving the Effect of Transcranial Alternating Current Stimulation (tACS): A Systematic Review

“…Neubauer combined θ tACS with fMRI to analyze the brain changes induced by prickles (Neubauer et al, 2017 ). Chen analyzed the role of 10-Hz and 20-Hz tACS in the integration and isolation of chronic stroke networks by fMRI (Chen et al, 2021 ). These studies point out a direction for us to explore the mechanism of tACS from various angles in the future.…”

Driving Oscillatory Dynamics: Neuromodulation for Recovery After Stroke

“…Studies using tACS have already shown increases in cerebral blood flow in both hemispheres and lowered resistance in the intracranial vascular bed in patients during the acute phase to 3 months after stroke (Salinet et al, 2014;Wu et al, 2016). Patients in the chronic phase after stroke have also shown network integration and segregation in both motor-related regions and on a whole-brain level after 10 and 20 Hz tACS stimulation (Chen et al, 2021). However, as with tDCS, more research is required to determine the mechanisms underlying the effects of tACS.…”

Effects of Transcranial Alternating Current Stimulation and Neurofeedback on Alpha (EEG) Dynamics: A Review

“…In comparison to the other EEG frequencies, EEG having the same or very similar frequency to tACS showed the greatest increase in amplitude when stimulated by tACS (Ali et al, 2013 ; Schmidt et al, 2014 ). Nevertheless, there is still a gap of knowledge related to the precise mechanisms responsible for the effects of tACS on brain activity as current evidence speaking in favor of the aforementioned tACS mechanisms are rather indirect (Zaehle et al, 2010 ; Krause et al, 2019 ; Chen et al, 2021 ; Frohlich and Townsend, 2021 ).…”

“…The effects of tACS or NFB on brain plasticity have been already investigated by using fMRI (Kluetsch et al, 2014 ; Nicholson et al, 2016 ; Abellaneda-Pérez et al, 2020 ; Gundlach et al, 2020 ; Mondino et al, 2020 ; Chen et al, 2021 ), the measurement of a motor-evoked potential (MEP) by transcranial magnetic stimulation (TMS) (Ros and Gruzelier, 2011 ; Wach et al, 2013 ; Vallence et al, 2021 ). The link between EEG changes and changes in the levels of the concentration of the molecular substrates of plasticity after tACS/NFB intervention has been already studied too Lee et al, 2019 ; Wischnewski et al, 2019 ; Markiewicz and Dobrowolska, 2020 ; Riddle et al, 2020a ).…”