Neurodynamic correlates for the cross-frequency coupled transcranial alternating current stimulation during working memory performance

Abstract

Transcranial current stimulation is a neuromodulation technique used to modulate brain oscillations and, in turn, to enhance human cognitive function in a non-invasive manner. This study investigated whether cross-frequency coupled transcranial alternating current stimulation (CFC-tACS) improved working memory performance. Participants in both the tACS-treated and sham groups were instructed to perform a modified Sternberg task, where a combination of letters and digits was presented. Theta-phase/high-gamma-amplitude CFC-tACS was administered over electrode F3 and its four surrounding return electrodes (Fp1, Fz, F7, and C3) for 20 min. To identify neurophysiological correlates for the tACS-mediated enhancement of working memory performance, we analyzed EEG alpha and theta power, cross-frequency coupling, functional connectivity, and nodal efficiency during the retention period of the working memory task. We observed significantly reduced reaction times in the tACS-treated group, with suppressed treatment-mediated differences in frontal alpha power and unidirectional Fz-delta-phase to Oz-high-gamma-amplitude modulation during the second half of the retention period when network analyses revealed tACS-mediated fronto-occipital dissociative neurodynamics between alpha suppression and delta/theta enhancement. These findings indicate that tACS modulated top-down control and functional connectivity across the fronto-occipital regions, resulting in improved working memory performance. Our observations are indicative of the feasibility of enhancing cognitive performance by the CFC-formed tACS.

Resting-state electroencephalographic characteristics related to mild cognitive impairments

“…Intuitively, nodal efficiency captures how efficiently information can be transmitted from a given node to the rest of the network through its immediate neighbors. A node with high nodal efficiency can communicate effectively with other nodes in the network, whereas a node with low nodal efficiency may be relatively isolated from the other nodes of the network ( 72 , 73 ).…”

Cross-Frequency Coupling and Intelligent Neuromodulation

“…[ 81 ] used optogenetic stimulation to restore memory performance and hippocampal θ – γ PAC in a mouse model of AD. Transcranial alternating current stimulation (tACS) has been recently shown to modulate top-down control and functional connectivity ( θ – γ coupling) across the frontal-occipital regions, leading to enhanced performance in working memory tasks [ 82 ]. Of note, stimulations at the θ – γ frequency over the trough have been found to impair cognitive control [ 83 ].…”

No effects of the theta-frequency transcranial electrical stimulation for recall, attention control, and relation integration in working memory

“…As WM mechanisms are frequently associated with patterns of neural oscillations (Axmacher et al, 2010 ; Palva et al, 2010 ; Lisman and Jensen, 2013 ; Roux and Uhlhaas, 2014 ; Sauseng et al, 2019 ), the tACS technique has been especially popular in the ongoing attempts to enhance WM. A number of tACS studies (e.g., Hoy et al, 2015 ; Alekseichuk et al, 2016 ; Feurra et al, 2016 ; Santarnecchi et al, 2016 ; Tseng et al, 2016 ; Möller et al, 2017 ; Borghini et al, 2018 ; Pahor and Jaušovec, 2018 ; Misselhorn et al, 2020 ; Thompson et al, 2021 ; Kim et al, 2022 ; Palm et al, 2022 ; Park et al, 2022 ; Zeng et al, 2022 ; Grover et al, 2023 ; Kvašnák et al, 2023 ) targeted the fast rhythms, such as the gamma (>30 Hz) and, more rarely, the beta band (14 Hz−30 Hz), following the fact that coordinated fast oscillations were linked with active maintenance of particular objects in WM (e.g., Lisman and Jensen, 2013 ; Leszczyński et al, 2015 ). Several such studies reported positive effects of stimulation on WM (e.g., Hoy et al, 2015 ; Alekseichuk et al, 2016 ).…”