After-effects of 10 Hz tACS over the prefrontal cortex on phonological word decisions

Abstract

Introduction: Previous work in the language domain has shown that 10 Hz rTMS of the left or right posterior inferior frontal gyrus (pIFG) in the prefrontal cortex impaired phonological decision-making, arguing for a causal contribution of the bilateral pIFG to phonological processing. However, the neurophysiological correlates of these effects are unclear. The present study addressed the question whether neural activity in the prefrontal cortex could be modulated by 10 Hz tACS and how this would affect phonological decisions. Methods: In three sessions, 24 healthy participants received tACS at 10 Hz or 16.18 Hz (control frequency) or sham stimulation over the bilateral prefrontal cortex before task processing. Resting state EEG was recorded before and after tACS. We also recorded EEG during task processing. Results: Relative to sham stimulation, 10 Hz tACS significantly facilitated phonological response speed. This effect was task-specific as tACS did not affect a simple control task. Moreover, 10 Hz tACS significantly increased theta power during phonological decisions. The individual increase in theta power was positively correlated with the behavioral facilitation after 10 Hz tACS. Conclusion: Our results show a facilitation of phonological decisions after 10 Hz tACS over the bilateral prefrontal cortex. This might indicate that 10 Hz tACS increased task-related activity in the stimulated area to a level that was optimal for phonological performance. The significant correlation with the individual increase in theta power suggests that the behavioral facilitation might be related to increased theta power during language processing.

The Modulation of Cognitive Performance with Transcranial Alternating Current Stimulation: A Systematic Review of Frequency-Specific Effects

“…On the contrary, alpha-tACS impaired visual and phonological discrimination performance [44,45]. Some frequencies led to no performance changes with online stimulation (i.e., theta-and beta-tACS) [52,54]. Online stimulation aiming to influence phase coherence (see Figure 1C; here: anti-phase, bi-hemispheric gamma-tACS) impaired visual motion change detection.…”

“…Moliadze and colleagues [52] applied alpha-tACS preceding a phonological decision task. The participants listened to words and decided whether they consisted of two or three syllables.…”

Modulating Inhibitory Control Processes Using Individualized High Definition Theta Transcranial Alternating Current Stimulation (HD θ-tACS) of the Anterior Cingulate and Medial Prefrontal Cortex

“…We used the optimal electrode arrangement based on computational modeling from individual MRIs to target the current flow with the highest specificity at the mPFC-ACC, with maximum current density in the ACC, to investigate the post-modulatory θ-tACS effect on inhibitory control. Based on the evidence from previous studies that confirmed the alteration of inhibitory control performance during θ-tACS neuromodulation (van Driel et al, 2015;Moliadze et al, 2019), we extended the experiment to include a θ-tACS condition that modulated the ACC indirectly through MFC.…”

“…Transcranial Alternating Current Stimulation (tACS) enables modulation of endogenous oscillations at the pacing rate (Paulus, 2011;Ali et al, 2013;Antal and Paulus, 2013;Herrmann et al, 2013;Antal and Herrmann, 2016), inducing frequency-specific activity changes (Vossen et al, 2015;Witkowski et al, 2016) and the subsequent induction of synaptic changes via neuronal plasticity, providing a post-modulation effect on brain oscillation activity (Antal et al, 2008;Zaehle et al, 2010;Vossen et al, 2015;Berger et al, 2018;Moliadze et al, 2019). The effect of various tACS frequencies on cognition was tested (Sela et al, 2012;Hoy et al, 2015;van Driel et al, 2015;Vosskuhl et al, 2015;Wischnewski et al, 2016;Fusco et al, 2018;Pahor and Jaušovec, 2018;Lehr et al, 2019;Moliadze et al, 2019). Specific cognitive abilities were significantly modified mostly by the theta frequency tACS (θ-tACS; Sela et al, 2012;van Driel et al, 2015;Vosskuhl et al, 2015;Wischnewski et al, 2016;Fusco et al, 2018Fusco et al, , 2020Pahor and Jaušovec, 2018;Lang et al, 2019;Lehr et al, 2019).…”

Lacking Effects of Envelope Transcranial Alternating Current Stimulation Indicate the Need to Revise Envelope Transcranial Alternating Current Stimulation Methods

“… 17 - 19 In particular, the immediate effects and sustained after effects of tACS on alpha activity have been well established. 20 - 24 In auditory research, tACS has been useful in making causal connections between brain activity and the hearing process; where brain recording methods can only infer correlation between neural entrainment and cognitive processes, 25 tACS makes it possible to infer causal links between the 2 by enhancing or disrupting entrainment to a certain frequency. 26 , 27 Using these methods, evidence has been found that neural entrainment plays an active role in speech perception, instead of merely being a result of it.…”