Non-invasive temporal interference electrical stimulation of the human hippocampus
Inês R. Violante, Ketevan Alania, Antonino M. Cassarà, Esra Neufeld, Emma Acerbo, Adam Williamson, Danielle L. Kurtin, E. J. Rhodes, Adam Hampshire, Niels Kuster, Edward S. Boyden, Álvaro Pascual‐Leone, Nir Grossman
Abstract
Abstract Temporal interference (TI) electrical stimulation is a novel method that allows a non-invasive targeting of neurons at depth. This is achieved by applying multiple kHz-range electric fields with a difference frequency within the range of natural rhythmic brain activity. Interference between these fields results in envelope modulation of electric fields at the difference frequency, causing neurons to engage at this range. Here, we show the first evidence of non-invasive and selective modulation of human hippocampal activity and dependent memory processes using transcranial TI stimulation. In experiment 1, we delivered transient TI stimulation to twenty healthy volunteers while they performed an episodic memory task inside a scanner and measured blood oxygen level-dependent (BOLD) activity at the same time. In three conditions, the locus of TI was focused on the left hippocampus, steered towards its anterior segment during memory encoding or switched off in the sham condition. We show that steering TI to the anterior hippocampus led to a reduction in task-evoked BOLD signal during memory encoding. No changes were observed in cortical regions underneath the electrodes. In experiment 2, we tested the effect of prolonged TI stimulation (∼ 30 min) on hippocampal function in a similar cohort. Active and sham (separate visits) TI stimulation conditions were delivered to the anterior left hippocampus while participants performed the same episodic memory task employed in experiment 1, with added trials. The TI stimulation of the hippocampus led to increased memory recall accuracy compared to sham. Our findings demonstrate the efficacy of TI stimulation to non-invasively modulate hippocampal activity and related function. Research Category and Technology and Methods Translational Research: 8. Transcranial Alternating Current Stimulation (tACS) Keywords: temporal interference, electrical stimulation, non-invasive, deep brain stimulation