Objective: We compared personalized MRI-based simulations of multi-electrode tACS with simulations using a fixed, standardized setting computed on the MNI head model in patients with mild cognitive impairment (MCI), as well as in healthy older (HO) and younger (HY) participants. We questioned whether the distribution and strength of the induced electrical field would differ among these three groups.

Methods: Structural MRI scans were acquired from 149 participants, including 33 MCI patients, 58 HY, and 58 HO adults. A fixed selection of 6 electrode positions was used to define the optimal current to induce an electric field strength of 0.3 V/m in the target region, the left angular gyrus. The distribution of the electric field strength in the brain, including the target region, was calculated for the personalized and standardized simulation conditions.

Results: Personalized tACS simulations showed a significantly increased electric field strength in the target region compared to the standardized simulation in MCI patients, the former being closer to the desired electric field strength. No difference was found in healthy participants. Moreover, the standardized simulation significantly increased the current variability at the target region compared to personalized simulations in all groups, indicating a larger current spread.

Conclusion: This study demonstrates that personalized modelling of electric fields is essential for controlling anatomical differences, ensuring accurate dosing in target regions, and minimizing the spread of stimulation to other areas, especially in individuals with MCI.

Significance: Anatomical variations can significantly impact the electrical field strength induced by transcranial electrical stimulation (tACS) in the brain of MCI patients.