Modulation of Sustained Attention by Theta-tACS over the Lateral and Medial Frontal Cortices

Abstract

Theta oscillations over the posterior medial frontal cortex (pMFC) and lateral prefrontal cortex (LPFC) play vital roles in sustained attention. Specifically, pMFC power and pMFC-LPFC synchronization correlate with cognitive control in sustained-attention-related tasks, but the causal relationships remain unknown. In the present study, we first analyzed the correlation between EEG theta oscillations (characterized by time-frequency power and phase-based connectivity) and the level of sustained attention (Experiment 1) and then utilized transcranial alternating current stimulation (tACS) to modulate theta oscillations and in turn observed its effects on sustained attention (Experiment 2). In Experiment 1, two time-frequency regions of interest (ROIs) were determined, in which high/low time-frequency power and high/low phase-based connectivity corresponded to high/low-level sustained attention. In Experiment 2, time-frequency power and phase-based connectivity of theta oscillations were compared between the sham and tACS groups within the time-frequency ROIs determined in Experiment 1. Results showed that phase-based connectivity between pMFC and LPFC significantly decreased in the tACS group compared with the sham group during the first five minutes of the poststimulation period. Moreover, a marginal trend existed that sustained attention was downregulated by tACS in the same time interval, suggesting that theta phase synchronization between pMFC and LPFC may play a causal role in sustained attention.

Advances in Non-Invasive Neuromodulation Techniques for Improving Cognitive Function: A Review

“…The results showed that at least one cognitive function improved following tACS in all cognitive areas, which is largely consistent with the study hypothesis. tACS of 6 Hz and 1 mA for 15 min was applied to the left DLPFC of the subjects, and through the use of a psychomotor vigilance task (PVT) and EEG analysis, it was found that compared with the sham stimulation group, the phase synchronization of the θ band following stimulation was significantly reduced in the true stimulation group, thus adjusting the sustained attention in the cognitive domain [26]. Varastegan et al [27] also subjected 16 elderly individuals with subjective memory complaints (SMC) to 6 Hz tACS, evaluated and recorded using the Rey Auditory-Verbal Learning Test (RAVLT), and found that θ-tACS could improve cognitive components such as event memory in SMC patients through activity in the frontal and temporal regions of the brain.…”