Inconsistencies in mapping current distribution in transcranial direct current stimulation

• Published in: Frontiers in neuroimaging Vol. 1; p. 1069500
• Main Authors: Jwa, Anita S., Goodman, Jonathan S., Glover, Gary H.
• Format: Journal Article
• Language: English
• Published: Switzerland Frontiers Media S.A 16.01.2023
• Subjects: current mapping; functional magnetic resonance imaging; Neuroimaging; non-invasive neuromodulation; transcranial direct current stimulation; transcranial electrical stimulation; non-invasive neuromodulation; transcranial electrical stimulation; functional magnetic resonance imaging; transcranial direct current stimulation; current mapping
• ISSN: 2813-1193; 2813-1193
• DOI: 10.3389/fnimg.2022.1069500

tDCS is a non-invasive neuromodulation technique that has been widely studied both as a therapy for neuropsychiatric diseases and for cognitive enhancement. However, recent meta-analyses have reported significant inconsistencies amongst tDCS studies. Enhancing empirical understanding of current flow in the brain may help elucidate some of these inconsistencies. We investigated tDCS-induced current distribution by injecting a low frequency current waveform in a phantom and . MR phase images were collected during the stimulation and a time-series analysis was used to reconstruct the magnetic field. A current distribution map was derived from the field map using Ampere's law. The current distribution map in the phantom showed a clear path of current flow between the two electrodes, with more than 75% of the injected current accounted for. However, in brain, the results did evidence a current path between the two target electrodes but only some portion ( 25%) of injected current reached the cortex demonstrating that a significant fraction of the current is bypassing the brain and traveling from one electrode to the other external to the brain, probably due to conductivity differences in brain tissue types. Substantial inter-subject and intra-subject (across consecutive scans) variability in current distribution maps were also observed in human but not in phantom scans. An current mapping technique proposed in this study demonstrated that much of the injected current in tDCS was not accounted for in human brain and deviated to the edge of the brain. These findings would have ramifications in the use of tDCS as a neuromodulator and may help explain some of the inconsistencies reported in other studies.