The structural effects of transcranial magnetic stimulation on hippocampal subfields in Alzheimer's disease

Aim: This study investigates the structural effects of repetitive transcranial magnetic stimulation (rTMS) on hippocampal subfields and cortical shape metrics in Alzheimer’s disease (AD) patients. Using high-resolution MRI segmentation and analysis via Hippunfold, we aim to elucidate TMS-induced structural changes and assess its potential neuroprotective role. Methods: This retrospective study included 17 AD patients and 18 healthy controls (HC). AD patients underwent 20 Hz rTMS targeting the left lateral parietal cortex over 10 sessions across two weeks. Magnetic resonance imaging (MRI) data were acquired before and after rTMS and analyzed with Hippunfold to segment hippocampal subfields and extract cortical thickness and shape metrics. Statistical analyses were performed to compare subfield volumes and cortical metrics between groups and across time points. Results: Hippocampal volumetric analysis revealed significant atrophy in subfields such as Cornu Ammonis 1, (CA1), CA2, CA4, dentate gyrus (DG), subiculum, and stratum radiatum-lacunosum-moleculare (SRLM) in AD patients compared to HC. Although no significant volumetric recovery was observed post-TMS, a further decline was noted in the right CA3 subfield (p=0.005), highlighting progressive atrophy. Cortical shape analyses showed significant reductions in hippocampal thickness (p