Authors :
Presenting Author: Richard Hou, Undergraduate Student – Emory College of Arts and Sciences
Emma Emma Acerbo, PhD – Emory University
Ken Berglund, PhD – Emory University
Nealen Laxpati, MD, PhD – Emory University School of Medicine
Claire-Anne Gutenkust, PhD – Emory University
Rationale:
Temporal Interference (TI) stimulation is an emerging, non-invasive alternative to Deep Brain Stimulation (DBS) for treating neurological disorders such as epilepsy. By applying two high-frequency electric fields with slight frequency offsets through scalp electrodes, TI generates low-frequency amplitude-modulated waveforms capable of targeting deep brain structures while sparing surrounding tissues. However, concerns about potential tissue damage during high-amplitude, low-frequency modulation remain as previous studies have shown that low-frequency modulation can produce lesions in the brain tissue. In this study, we assessed safety of TI stimulation using in vitro as well as in vivo models.
Methods:
An egg white model—chosen for its protein similarity to brain tissue—was first used for a preliminary evaluation of coagulation risk. TI stimulation (1 kHz and 1.005 kHz, 10 mA, yielding a 5 Hz amplitude-modulated signal) was applied for 20 minutes. This was compared to conventional low-frequency transcranial alternating current stimulation (tACS; 5 Hz, 10 mA, 20 minutes).
Subsequent in vivo validation was conducted in mice, targeting the left hippocampus with TI stimulation (1 kHz and 1.005 kHz, 2 mA, 20 minutes). One cohort (n=4) was monitored for temperature changes using a thin temperature probe, while another cohort used to assess the tissue response to TI using histological markers. This second cohort was divided into three groups: TI, Sham, and Control. The TI group received the same stimulation parameters as the temperature cohort. The Sham group underwent stimulation with two identical 1 kHz carrier waveforms, thereby generating no amplitude modulated signal. The Control group had electrodes placed without no current applied. 24 hrs post-stimulation, mice were perfused and brain collected for subsequent immunostaining using markers of injury (GFAP), heat stress response (HSP70), and vasodilation/inflammation (iNOS). Expression levels were quantified using ImageJ and compared between groups.
Results:
In the egg white model, TI stimulation did not produce apparent coagulation, whereas low frequency tACS did result in localized lesions. In mice, TI stimulation induced only a mild temperature increase (~0.7°C) at the stimulation site. Immunohistochemical analysis revealed increased GFAP expression in the stratum lacunosum-moleculare (SLM) of the hippocampus, indicating potential localized injury. However, minimal HSP70 and iNOS expression suggested a lack of significant thermal stress or inflammatory/vasodilatory responses.
Conclusions:
TI stimulation demonstrates minimal thermal effects and does not provoke widespread inflammatory or injury responses in brain tissue, supporting its safety profile for potential use in epileptic patients. While some localized tissue reactivity (GFAP) was observed, the absence of significant heat or inflammatory markers suggests that TI may be safe for deep brain targeting, pending further investigation.
Funding: Emory University Undergraduate Independent Research Grant to RH and NIH-NINDS 1R01NS138733-01 to CAG and KB.