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Postdoctorial Fellowship Award Winner 

Hippocampal modulation via indirectly targeted noninvasive stimulation is intensity-dependent and region-selective

Poster Session C - Sunday, March 8, 2026, 5:00 – 7:00 pm PDT, Fairview/Kitsilano Ballroom
Also presenting in Data Blitz Session 1 - Saturday, March 7, 2026, 10:30 am – 12:00 pm PST, Salon ABC.

Arantzazu San Agustín¹ (), Robert B. Baudo¹, Johanna M.H. Rau¹, James E. Kragel¹, Joel L. Voss¹; ¹University of Chicago

How can hippocampal activity be modulated via noninvasive stimulation? Hippocampal Indirectly Targeted Stimulation (HITS) modulates hippocampal activity applying transcranial magnetic stimulation (TMS) to accessible locations of the hippocampal network in parietal cortex. HITS enhances memory performance and hippocampal connectivity measured via fMRI, yet the temporal electrophysiological dynamics of hippocampal responses mediating these effects remain unknown. Characterizing HITS-induced hippocampal activity with high temporal precision allows assessment of how stimulation intensity and location shape hippocampal dynamics, advancing our knowledge in underlying memory mechanisms and providing a framework to refine time-specific noninvasive neuromodulation strategies. We hypothesize that HITS evokes stronger hippocampal responses than out-of-network or sham stimulation, with effects increasing by intensity but losing selectivity at high intensity levels. We tested this hypothesis in N=4 individuals with refractory epilepsy implanted with intracranial electrodes in hippocampus and parahippocampal gyrus (n=28 contacts). We applied TMS at 60%, 80%, 100%, and 120% of resting motor threshold under HITS, sham, and out-of-network (in S1) stimulation conditions. In a subset of the sample, HITS intensity produced progressively larger intracranial potentials immediately after TMS (p = .04; 4–62 ms) and more negative amplitudes later (p = .04; 488–576 ms). HITS responses were significantly more negative than sham and S1 at 100% intensity (p < .01; 385–509 ms). These results provide direct evidence of hippocampal responses to HITS and how they can be modulated in an intensity-dependent and region-selective manner. These results advance understanding of TMS effects on hippocampal activity and may contribute to developing effective noninvasive memory modulation strategies.

Topic Area: LONG-TERM MEMORY: Episodic