Bifocal tACS Enhances Visual Motion Discrimination by Modulating Phase Amplitude Coupling Between V1 and V5 Regions

Abstract

Visual motion discrimination involves reciprocal interactions in the alpha band between the primary visual cortex (V1) and the mediotemporal area (V5/MT). We investigated whether modulating alpha phase synchronization using individualized multisite transcranial alternating current stimulation (tACS) over V5 and V1 regions would improve motion discrimination. We tested 3 groups of healthy subjects: 1) an individualized In-Phase V1alpha-V5alpha tACS (0° lag) group, 2) an individualized Anti-Phase V1alpha-V5alpha tACS (180° lag) group and 3) a sham tACS group. Motion discrimination and EEG activity were compared before, during and after tACS. Performance significantly improved in the Anti-Phase group compared to that in the In-Phase group at 10 and 30 minutes after stimulation. This result could be explained by changes in bottom-up alpha-V1 gamma-V5 phase-amplitude coupling. Thus, Anti-Phase V1alpha-V5alpha tACS might impose an optimal phase lag between stimulation sites due to the inherent speed of wave propagation, hereby supporting optimized neuronal communication.IMPACT STATEMENTAlpha multisite (V1 and V5) tACS influences global motion discrimination and integrationPhase-amplitude coupling is associated with visual performanceMultisite Anti-Phase stimulation of strategic visual areas (V1 and V5) is associated with connectivity changes in the visual cortex and thus, associated with changes in direction acuity

Modulating verbal working memory with fronto‐parietal transcranial electric stimulation at theta frequency: Does it work?

“…Interestingly, while we could not reproduce a ‘synchronization‐desynchronization’ effect by fronto‐parietal theta tACS on response times in a delayed letter recognition task, we could show that in a more demanding 3‐back task, in‐phase and in‐phase focal theta tACS improved discriminability substantially compared to a sham condition. A ‘synchronization‐desynchronization’ effect through in‐phase or anti‐phase tACS was reproduced, at least partly, both for working memory by fronto‐parietal theta tACS (Alekseichuk et al, 2017; Röhner et al, 2018; Tseng et al, 2018; Violante et al, 2017) but also for other cognitive domains; such as for semantic retrieval performance by fronto‐parietal theta tACS (Marko et al, 2019), for executive functions by frontal theta tACS (Reinhart, 2017), for spatial attention by fronto‐parietal alpha tACS (van Schouwenburg et al, 2017), or for motion perception through parieto‐occipital gamma and alpha tACS (Helfrich et al, 2014; Salamanca‐Giron et al, 2020; Strüber et al, 2014). Especially those studies reporting an improvement in working memory performance for older adults and low‐performing individuals (Reinhart & Nguyen, 2019; Tseng et al, 2016, 2018) are quite promising for future therapeutic applications.…”

“…However, it is challenging that results have been relatively inconsistent so far. And, intriguingly, behavioural modulation due to anti‐phase stimulation has sometimes been characterized by an enhancement effect on performance instead of showing detrimental effects (Salamanca‐Giron et al, 2020; Tseng et al, 2016; Yaple & Vakhrushev, 2018). Depending on the actual phase lag between two stimulated brain areas, either in‐phase or anti‐phase stimulation might be most beneficial.…”

Targeting the fronto-parietal network using multifocal personalized transcranial alternating current stimulation to enhance motor sequence learning in healthy older adults

“…Recordings were done during 3 N-back blocks resulting in approximately 3 minutes of recording time. The peak frequency in the theta range (4 – 8 Hz) was calculated using a custom Matlab script (The MathWorks Inc., USA) adapted from the script used by Salamanca-Giron and colleagues [54] and made suitable for theta frequency analysis during N-back task performance.…”

Targeting the frontoparietal network using bifocal transcranial alternating current stimulation during a motor sequence learning task in healthy older adults

“…Participants received both real (30 min) or sham (30 s) stimulation in randomized order, before or after cross-over [24,25,53]. The stimulation protocol consisted of the following parameters: in-phase (0⁰ phase lag), intensity 2 mA (peak-to-peak) was gradually ramped up/down with an interval of 8 s. The in-phase stimulation between the two stimulators was assured by a repeated trigger from stimulator A to stimulator B after every completed cycle to signal the start of a new cycle [54]. The stimulation frequency was adjusted to the personal theta peak frequency, which was recorded during an EEG recording while performing a pre-baseline N-back test of 1 block per level.…”

“…Recordings were done during 3 N-back blocks resulting in approximately 3 min of recording time. The peak frequency in the theta range (4e8 Hz) was calculated using a custom Matlab script (The MathWorks Inc., USA) adapted from the script used by Salamanca-Giron and colleagues [54] and made suitable for theta frequency analysis during N-back task performance. Theta frequencies for tACS were personalized similar to previous work [54,57].…”