Multimodal Evidence for Hippocampal Engagement and Modulation by Functional Connectivity-Guided Parietal TMS

Hippocampal activity supports memory and many other brain functions. Transcranial magnetic stimulation (TMS) guided by hippocampal functional connectivity (FC) shows promise in improving memory, but direct neural evidence of its capacity to engage and modulate hippocampal activity is lacking. Here we combined TMS with intracranial electroencephalography (iEEG) in 8 neurosurgical patients and with functional magnetic resonance imaging (fMRI) in 79 neurologically healthy participants. We identified that (1) single-pulse TMS to individualized parietal cortex guided by hippocampal-FC preferentially evoked distinct temporal and spectral activity patterns in the hippocampus, (2) variability in TMS-evoked hippocampal responses related to individual differences in parietal-hippocampus FC strength, and (3) repetitive TMS to hippocampal-FC-guided parietal cortex selectively suppressed hippocampal theta oscillations. These findings provide multimodal causal neural evidence and important mechanistic insights supporting the development of personalized neuromodulation strategies aimed at improving hippocampus-dependent functions.