# Safety assessment of temporal interference stimulation

## TL;DR

This study evaluates the safety of temporal interference stimulation in the brain, finding minimal thermal effects and no significant inflammation.

## Contribution

The study provides the first in vivo and in vitro safety assessment of temporal interference stimulation targeting deep brain regions.

## Key findings

- TI stimulation at 10 mA did not cause protein coagulation in an egg-white model, unlike conventional tACS.
- In mice, TI stimulation caused a mild temperature increase of ~0.7°C in the hippocampus without significant heat stress or inflammation.
- Localized astrocyte activation was observed in the stratum lacunosum-moleculare but not in other hippocampal regions.

## Abstract

Temporal interference (TI) stimulation is a promising non-invasive neuromodulation strategy that uses two high-frequency electric fields to generate a low-frequency amplitude-modulated envelope at their intersection, enabling targeting of deep brain regions. However, in vivo safety concerns remain regarding the impact of the low-frequency envelope applied to the brain. Therefore, the objective of this study was to systematically evaluate the acute thermal and cellular safety profile of TI using an invasive in vivo mouse model, and to compare its thermal effects with those of direct low-frequency stimulation using an in vitro egg-white model. In the egg-white model, no protein coagulation was observed with TI stimulation (10 mA at 1,000 Hz and 1,005 Hz for 20 min), which generated a 5 Hz envelope. In contrast, conventional 5 Hz alternating current stimulation (tACS) at 10 mA induced localized coagulation. In the mouse model, intracranial TI stimulation (2 mA at 1,000 Hz and 1,005 Hz for 20 min) targeting the hippocampus resulted in a mild and stable temperature increase of ∼0.7 °C. Histological analysis revealed a localized increase in astrocyte activation (GFAP) in the stratum lacunosum-moleculare (SLM) compared to other hippocampal subfields. No significant expression difference was observed in the hippocampus for the heat stress marker (HSP70) or the inflammatory marker (iNOS). These findings suggest that TI has a favorable short-term safety profile, with minimal thermal effects and no widespread inflammatory response.