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Impact of brain atrophy on tDCS and HD-tDCS current flow: a modeling study in three variants of primary progressive aphasia



During transcranial direct current stimulation (tDCS), the amount and distribution of current that reaches the brain depends on individual anatomy. Many progressive neurodegenerative diseases are associated with cortical atrophy, but the importance of individual brain atrophy during tDCS in patients with progressive atrophy, including primary progressive aphasia (PPA), remains unclear.


In the present study, we addressed the question whether brain anatomy in patients with distinct cortical atrophy patterns would impact brain current intensity and distribution during tDCS over the left IFG.


We developed state-of-the-art, gyri-precise models of three subjects, each representing a variant of primary progressive aphasia: non-fluent variant PPA (nfvPPA), semantic variant PPA (svPPA), and logopenic variant PPA (lvPPA). We considered two exemplary montages over the left inferior frontal gyrus (IFG): a conventional pad montage (anode over F7, cathode over the right cheek) and a 4 × 1 high-definition tDCS montage. We further considered whether local anatomical features, specifically distance of the cortex to skull, can directly predict local electric field intensity.


We found that the differences in brain current flow across the three PPA variants fall within the distribution of anatomically typical adults. While clustering of electric fields was often around individual gyri or sulci, the minimal distance from the gyri/sulci to skull was not correlated with electric field intensity.


Limited to the conditions and assumptions considered here, this argues against a specific need to adjust the tDCS montage for these patients any more than might be considered useful in anatomically typical adults. Therefore, local atrophy does not, in isolation, reliably predict local electric field. Rather, our results are consistent with holistic head anatomy influencing brain current flow, with tDCS producing diffuse and individualized brain current flow patterns and HD-tDCS producing targeted brain current flow across individuals.

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We would like to thank our participants and referring physicians for their dedication and interest in our study.


This work was supported through the National Institutes of Health: NIH–NINDS 1R01NS101362, NIH–NIMH 1R01MH111896 to MB and by the National Institutes of Health (National Institute of Deafness and Communication Disorders) through award R01 DC014475 to KT.

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Correspondence to Kyrana Tsapkini.

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The City University of New York has patents on Brain Stimulation with MB as inventor. MB has equity in Soterix Medical and serves on the Boston Scientific and GlaxoSmithKline scientific advisory boards.

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The study was approved by Johns Hopkins University IRB.

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Unal, G., Ficek, B., Webster, K. et al. Impact of brain atrophy on tDCS and HD-tDCS current flow: a modeling study in three variants of primary progressive aphasia. Neurol Sci (2020). https://doi.org/10.1007/s10072-019-04229-z

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  • HD-tDCS
  • Conventional tDCS
  • Primary progressive aphasia
  • Electrical current flow
  • Modeling
  • Atrophy