Effect of combined yoga and transcranial direct current stimulation intervention on working memory and mindfulness

Abstract

Transcranial direct stimulation, a non-invasive neurostimulation technique for modulating cortical excitability, and yoga have both respectively been shown to positively affect cognition. While preliminary research has shown that combined transcranial direct stimulation and meditation may have synergistic effects on mood and cognition, this was the first study to explore the combination of transcranial direct stimulation and yoga. Twenty-two healthy volunteers with a regular yoga practice were randomized to receive either active transcranial direct stimulation (anodal left, cathodal right dorsolateral prefrontal cortex) followed by yoga intervention or sham transcranial direct stimulation followed by yoga intervention a double-blind, cross-over design over two separate intervention days. Outcome measures included working memory performance, measured with the n-back task and mindfulness state, measured with the Toronto Mindfulness Scale, and were conducted offline, with pre-post assessments. Twenty participants completed both days of the intervention. Active transcranial direct stimulation did not have a significant effect on working memory or levels of mindfulness. There was a significant placebo effect, with better performance on day 1 of the intervention, irrespective of whether participants received active or sham transcranial direct stimulation. There was no significant difference between active versus sham transcranial direct stimulation concerning working memory performance and mindfulness, which may be accounted by the small sample size, the transient nature of the intervention, the fact that yoga and transcranial direct stimulation concerning were not conducted simultaneously, and the specific site of stimulation.

Stimulated brains and meditative minds: A systematic review on combining low intensity transcranial electrical stimulation and meditation in humans

“…The published studies included 664 participants, after correcting for secondary analyses publications using the same participants, comprising of 56.93% females and 43.07% males ( Table 1 ). Seven out of the 20 studies were conducted in healthy individuals ( Badran et al, 2017 ; Clarke et al, 2020 ; Danilewitz et al, 2021 ; Hunter et al, 2018 ; Nishida et al, 2021 ; Robinson et al, 2019 ; Sefat et al, 2022 ), while the remaining studies tested the combination of tDCS and meditation in patient groups diagnosed with conditions such as chronic pain ( Ahn et al, 2019; Pimenta et al, 2021 ; Pollonini et al, 2020 ; Ramasawmy et al, 2022 ), psychological disorders ( Alizadehgoradel et al, 2021 ; Brooks et al, 2021 ; Brown et al, 2020 ; Gibson et al, 2022 ; Hung, 2019 ; Monnart et al, 2019 ; Witkiewitz et al, 2019 ), mild cognitive impairment ( Liao et al, 2021 ), and movement disorders ( Park et al, 2021 ). All the ongoing studies test the combined intervention in diseased populations ( Table 2 ).…”

“…2B ). In addition, four studies had a cross over design, with all participants receiving both sham and real tDCS protocols ( Badran et al, 2017 ; Danilewitz et al, 2021 ; Park et al, 2021 ; Sefat et al, 2022 ), while the remaining studies followed a parallel design ( Table 1 ).…”

“…The montages of electrode placement for the 20 published studies were very different ( Table 3 & 4 ). The most frequent montage was the left (anode, F3) and right (cathode, F4) dorsolateral prefrontal cortex (dlPFC) (25%, Alizadehgoradel et al, 2021 ; Danilewitz et al, 2021 ; Hung, 2019 ; Monnart et al, 2019 ; Sefat et al, 2022 ). Generally, most of the studies (95%) stimulated the frontal lobe with the exception being Park et al (2021) , who stimulated at the right temporoparietal junction (tPJ).…”

“…Along the same line of interest, Danilewitz et al (2021) and Sefat et al (2022) paired yoga with tDCS targeting WM. Danilewitz et al (2021) found that one session of yoga following anodal 2 mA (left dlPFC) tDCS failed to show any improvement on WM or mindfulness level compared to a sham session of yoga combined with sham tDCS in a cross-over design. However, a placebo effect was observed with higher WM performances after first session than second one.…”

“…However, a placebo effect was observed with higher WM performances after first session than second one. Sefat et al (2022) had a similar intervention design to Danilewitz et al (2021) , but rather, participants performed yoga prior to stimulation. Despite finding no significant differences in power spectral density, they found that anodal tDCS over the left dlPFC at 2 mA and yoga had significantly increased functional connectivity in the frontal lobe, as measured using EEG.…”