Advancing non-invasive brain stimulation: A CompreheNSive Study of Temporal Interference Mechanisms (CNS-STIM)

PROJECT SUMMARY/ABSTRACT Temporal Interference (TI) is an innovative non-invasive brain stimulation technique that holds great promise. It utilizes high-frequency electrical currents (e.g., 1000 Hz and 1000 + Δf Hz) to achieve deep and precise brain stimulation. TI is characterized by the simultaneous application of two high-frequency electrical signals, each

with a specific offset frequency (referred to as Δf). This combination results in the creation of an amplitude modulation (AM), at depth, considered to be the stimulating signal within the targeted brain structure. However, despite its theoretical potential and successful application in the peripheral nervous system, there are significant

gaps in our understanding of how TI truly functions within the central nervous system (CNS). To bridge this knowledge gap, this three-year research project is structured around three specific aims. Aim 1 delves into the spatial precision, focality, and depth of TI stimulation. We will examine the correlation between the size of AM

and its impact on neuronal activation using real-time calcium level monitoring in brain slices, finite element simulations, recording in anesthetized mice and expression of immediate early genes (IEGs - i.e., c-fos, c-jun, arc). Aim 2 explores the frequency of AM (Δf) generated by TI and its potential interaction with carrier

frequencies. We will use genetically encoded voltage indicators to study cellular dynamics (cell type specific response to TI stimulation i.e., glutamatergic, GABAergic) in brain slices on a microelectrode array. We will also examine the impact of varying Δf in vivo with the co-localization of neuronal subtype (glutamatergic vs GABAergic

cells) and IEGs. Aim 3 investigates the differential effects of TI on neurons and fibers within the CNS. We will grow primary neurons in microfluidic chambers to physically separate cell bodies from axons and compare soma versus axon targeted by TI in vitro. Additionally, by varying the orientation of electrode pairs in vivo, we will also

compare direct TI stimulation of specific nuclei (i.e., septum and hippocampus) versus stimulation of the pathways (i.e., septo-hippocampal and perforant). Finally, we will combine TI with reversible chemogenetic neuromodulation to reveal if TI stimulation is enhanced when targeting the pathways projecting to the specific

target structure, as opposed to directly stimulating the target itself. Through this multifaceted research, we aim to bridge the gap between TI's theoretical promise and its practical applications, ultimately advancing our understanding of non-invasive neuromodulation and its potential clinical implications.