Investigating the effect of brain atrophy on transcranial direct current stimulation: A computational study using ADNI dataset

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that uses weak electrical currents to modulate brain activity, thus potentially aiding the treatment of brain diseases. Although tDCS offers convenience, it yields inconsistent electric-field distributions among individuals. This inconsistency may be attributed to certain factors, such as brain atrophy. Brain atrophy is accompanied by increased cerebrospinal fluid (CSF) volume. Owing to the high electrical conductivity of CSF, its increased volume complicates current delivery to the brain, thus resulting in greater inter-subject variability. We aim to investigate the differences in tDCS-induced electric fields between groups with different severities of brain atrophy. We classified 180 magnetic resonance images into four groups based on the presence of Alzheimer's disease and sex. We used two montages, i.e., F-3 & Fp-2 and TP-9 & TP-10, to target the left rostral middle frontal gyrus and the hippocampus/amygdala complex, respectively. Differences between the groups in terms of regional volume variation, stimulation effect, and correlation were analyzed. Significant differences were observed in the geometrical variations of the CSF and two target regions. Electric fields induced by tDCS were similar in both sexes. Unique patterns were observed in each group in the correlation analysis. Our findings show that factors such as brain atrophy affect the tDCS results and that the factors present complex relationships. Further studies are necessary to better understand the relationships between these factors and optimize tDCS as a therapeutic tool.