I think it's for shutting down the internal monologue for people who can't do it by will. If you can do it yourself, do you know if shutting down your internal monologue also cuts back on habitual muscle tension?
shutting down internal monologue lower muscle tension by deactivation the negative part of limbic system
Fast track to pure focus
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That hasn't stopped a vibrant community of DIY tDCS enthusiasts from springing up. Their online forums are full of accounts of their home-made experiments, including hair-curling descriptions of blunders that, in one case, left someone temporarily blind.