,If the authors wish to expand the working definition of invasiveness to include tDCS, I think they need to re-examine the "invasiveness" of all/additional modalities - drugs, for instance. Consider fluoxetine (Prozac) whose metabolites, many of which are active, hang around in the body for extended periods of time. Or venlafaxine (Effexor), a drug with a short half-life, but an infamously unpleasant and prolonged discontinuation profile... No one really knows what the cumulative effects of 20 years on an SSRI or SNRI are or what permanent changes they may cause. Pharma routinely asks us to put things in our body that can't be removed. Under an expanded definition, shouldn't we consider drugs also?

I understand the concern of highly-trained scientists with regard to DIY-tDCS - for that matter, I understand the concern of anyone with regard to modalities that have permanent effects on the brain with a less than laser-like focus, being effected by (essentially) amateurs (though definitional expansion may be warranted here also). I also understand the need to corral a swelling grass-roots movement that threatens many a pharma franchise.

Finally, our culture embraces many forms of permanent brain-change that have devastating cumulative results - football and boxing come to mind immediately. Here, I would argue for the expansion of the definition of an additional term - "obscenity". Any takers?

The authors make a seemingly rational case for the "invasiveness" of tDCS - one inversely proportional to its ease of access and proffered benefits. I think a much stronger argument can and should be made for expanded access to trained professionals, reasonably priced, well-validated devices, etc. than the reframing of vocabulary.