Is Transcranial Alternating Current Stimulation Effective in Modulating Brain Oscillations?

Abstract

Transcranial alternating current stimulation (tACS) is a promising tool for modulating brain oscillations, as well as a possible therapeutic intervention. However, the lack of conclusive evidence on whether tACS is able to effectively affect cortical activity continues to limit its application. The present study aims to address this issue by exploiting the well-known inhibitory alpha rhythm in the posterior parietal cortex during visual perception and attention orientation. Four groups of healthy volunteers were tested with a Gabor patch detection and discrimination task. All participants were tested at the baseline and selective frequencies of tACS, including Sham, 6 Hz, 10 Hz, and 25 Hz. Stimulation at 6 Hz and 10 Hz over the occipito-parietal area impaired performance in the detection task compared to the baseline. The lack of a retinotopically organised effect and marginal frequency-specificity modulation in the detection task force us to be cautious about the effectiveness of tACS in modulating brain oscillations. Therefore, the present study does not provide significant evidence for tACS reliably inducing direct modulations of brain oscillations that can influence performance in a visual task.

Different coupling modes mediate cortical cross-frequency interactions

“…This is in line with several other recent studies, which also suggested that secondary effects might occur across different temporal scales in coupled or nested neuronal networks (Boyle and Fröhlich, 2013;Neuling et al, 2012;Wach et al, 2013). Thus, cross-frequency effects and co-modulations of coupled networks might explain previous equivocal findings in tACS studies (Brignani et al, 2013).…”

EEG oscillations: From correlation to causality

“…Laczó et al (2012) applied tACS at 40, 60, and 80 Hz over the visual cortex and found an increase of contrast perception only for 60 Hz stimulation. Whereas these studies were all able to demonstrate frequency-specific perceptual consequences of tACS, this pattern of results is not without exception (Brignani et al, 2013).…”

Does 10-Hz cathodal oscillating current of the parieto-occipital lobe modulate target detection?

“…In comparison to the classical rhythmic sensory stimulation protocols mentioned above which interacts with the entire visual system, the use of tCS offers the advantage of directly stimulating cortical targets (Brignani et al, 2013). The aim of the current study was to provide a proof of principle that the entrainment of ongoing neural oscillations by rhythmic visual stimulation can be replicated with cathodal otCS at the same frequency.…”

“…Although numerous studies have demonstrated that these electrical stimulation methods can effect perception (Antal et al, 2004b;Neuling et al, 2012a;Helfrich et al, 2014) and cognition (Marshall et al, 2006;Zaehle et al, 2011;Antonenko et al, 2016;Simonsmeier and Grabner, 2017), it seems that many other studies have found little to no evidence supporting the efficacy of these techniques (Brignani et al, 2013;Tremblay et al, 2014;Horvath et al, 2015;Marshall et al, 2016;Veniero et al, 2017). Therefore, here we used a well-studied paradigm of alpha oscillations affecting visual perception as a test of the feasibility of using tCS to manipulate oscillations and cognition.…”