Theta Phase-dependent Modulation of Perception by Concurrent Transcranial Alternating Current Stimulation and Periodic Visual Stimulation

Abstract

Sensory perception can be modulated by the phase of neural oscillations, especially in the theta and alpha ranges. Oscillatory activity in the visual cortex can be entrained by transcranial alternating current stimulation (tACS) as well as periodic visual stimulation (i.e., flicker). Combined tACS and visual flicker stimulation modulates BOLD response, and concurrent 4-Hz auditory click train, and tACS modulate auditory perception in a phase-dependent way. In this study, we investigated whether phase synchrony between concurrent tACS and periodic visual stimulation (i.e., flicker) can modulate performance on a visual matching task. Participants completed a visual matching task on a flickering visual stimulus while receiving either in-phase (0°) or asynchronous (180°, 90°, or 270°) tACS at alpha or theta frequency. Stimulation was applied over either occipital cortex or dorsolateral pFC. Visual performance was significantly better during theta frequency tACS over the visual cortex when it was in-phase (0°) with visual stimulus flicker, compared with antiphase (180°). This effect did not appear with alpha frequency flicker or with dorsolateral pFC stimulation. Furthermore, a control sham group showed no effect. There were no significant performance differences among the asynchronous (180°, 90°, and 270°) phase conditions. Extending previous studies on visual and auditory perception, our results support a crucial role of oscillatory phase in sensory perception and demonstrate a behaviorally relevant combination of visual flicker and tACS. The spatial and frequency specificity of our results have implications for research on the functional organization of perception.

Transcranial alternating current stimulation at theta frequency to the parietal cortex impairs associative, but not perceptual, memory encoding

“…However, tACS also improved correct rejections of lure items, which suggests a more general cognitive enhancement effect. Previous studies reported theta oscillatory activity in human and animal prefrontal and sensory cortex during working memory procedures (Lee et al, 2005; Raghavachari et al, 2006; Sauseng, Griesmayr, Freunberger, & Klimesch, 2010), as well as during perceptual processing (Helfrich et al, 2018; Landau, Schreyer, Van Pelt, & Fries, 2015; Somer, Allen, Brooks, Buttrill, & Javadi, 2020), which support the contribution of various cognitive processes to associative memory performance. Indeed, a number of studies reported enhanced working memory performance after theta tACS was administered over parietal (Jaušovec & Jaušovec, 2014) or prefrontal cortex (Alekseichuk, Turi, de Lara, Antal, & Paulus, 2016), while tACS-induced frontoparietal inter-regional desynchronization at 6 Hz resulted in decreased working memory performance (Alekseichuk, Pabel, Antal, & Paulus, 2017).…”

Discrete sampling in perception via neuronal oscillations—Evidence from rhythmic, non‐invasive brain stimulation

“…While the authors found indications that task performance was modulated by beta power, there was no significant modulation of task performance with the phase of the tACS waveform (Battaglini et al, 2020). Somer et al (2020) applied tACS in the theta frequency range concurrently with visual flicker (target stimuli changing color at the same frequency as tACS). When tACS was applied in-phase with the visual flicker, RTs needed to discriminate the flickering target stimuli were reduced as compared to anti-phase stimulation.…”

“…The effect was specific to occipital cortex stimulation (i.e., did not occur during the stimulation of the dorsolateral prefrontal cortex). Interestingly, the effect did not occur when the experiment was repeated with stimulation at alpha frequency (Somer et al., 2020).…”

“…Somer et al. (2020) applied tACS in the theta frequency range concurrently with visual flicker (target stimuli changing color at the same frequency as tACS). When tACS was applied in‐phase with the visual flicker, RTs needed to discriminate the flickering target stimuli were reduced as compared to anti‐phase stimulation.…”