Related Experiment Video
Updated: Apr 14, 2026
Neuronavigated Focalized Transcranial Direct Current Stimulation Administered During Functional Magnetic Resonance Imaging
Published on: November 15, 2024
2 mA is NOT 2 mA: Electric field variability in high-definition tDCS and its implications for precision
Alexandru D Iordan1, Patrick J Pruitt1, Robert Ploutz-Snyder2
1Research Program on Cognition and Neuromodulation Based Interventions (RP-CNBI), Department of Psychiatry, University of Michigan, 4250 Plymouth Rd, Ann Arbor 48109, MI, USA.
Objective:
To evaluate intra- and inter-subject variability in electric field (EF) delivered by high-definition transcranial direct current stimulation (HD-tDCS) in neurologically mixed older adults, and test whether using multiple MRI sequences reduces variability.
Methods:
We used ROAST to simulate EF distributions for two HD-tDCS 4 × 1 montages in 442 adults (age 50-94) across the "normal" to dementia continuum. Individualized head models were built from structural MRI, using T1-weighted alone or T1T2 dual-contrast segmentation. Montages targeted left inferior frontal gyrus (IFG) or right superior parietal lobule (SPL). EF magnitude was extracted from anatomically defined grey matter regions (left IFG, right SPL).
Results:
EF magnitude varied by up to 400% across, and up to 35% within, individuals even after excluding segmentation and EF outliers. Left IFG consistently showed higher and more variable EF than the right SPL. Dual-contrast (T1T2) segmentation improved non-brain tissue delineation but EF variability persisted (up to 300%).
Conclusions:
Consonant with prior findings, 2 mA is NOT 2 mA within or across individuals, as delivered EF depends strongly on targeted region(s) and individual brain morphology.
Significance:
These findings reinforce the need for individualized modeling, especially for older and clinical populations, and for moving beyond scalp-based to delivered dose at brain level.
