Optimization of interferential stimulation of the human brain with electrode arrays

Abstract

Interferential stimulation (IFS) has generated considerable interest recently because of its potential to achieve focal electrical stimulation in deep brain areas despite applying currents transcranially. Conventionally, IFS applies sinusoidal currents through two electrode pairs with close-by frequencies.Here we propose to use two arrays of scalp electrodes with current intensity through each electrode optimized to target a desired location in the brain. We formulate rigorous optimization criteria for IFS to achieve either maximal modulation depth or most focal stimulation. For max-modulation optimization we show analytically that the solution is the same for IFS as for conventional multi-electrode stimulation. We proof that the solution can be found directly from the forward model without the need for algorithmic optimization. For the max-focality criterion the solution requires numerical optimization. Once optimized, we find that IFS can achieve more focal modulation of stimulation intensity than conventional stimulation with a single frequency, both at the cortical surface and deep in the brain.

High Gamma and Beta Temporal Interference Stimulation in the Human Motor Cortex Improves Motor Functions

“…Our study, for the first time, suggests that the idea of TI stimulation is plausible, not only in computational models and experiments on mice [27,[34][35][36][37][38], but also in actual experiments performed on healthy human participants. Since the idea of TI stimulation has been raised, the only in vivo investigations have been performed on mouse brains [27].…”

“…Based on the concept of TI stimulation, several modeling and computation studies have been performed to explore the feasibility of TI stimulation in the human brain but have revealed different results. Several studies reported that TI stimulation generated field strength in deep brain regions similar to tACS with smaller electric field intensity in superficial areas [34][35][36][37][38]. A computational modeling study explored the impact of TI stimulation on neuron levels but found that not all types of neurons responded to TI stimulation [39].…”

A Computational Study On The Optimization of Transcranial Temporal Interfering Stimulation With High-Definition Electrode Using Unsupervised Neural Network

“…1c). In this electrode system, the positions of all electrodes were assumed to produce two types of frequencies 26 .…”

“…When two different high-frequency currents are injected on both sides of the head, a beat with an interference frequency corresponding to the difference between the two frequencies is generated. The frequency of the injected current is that the human brain cannot recognize and the difference between the two frequencies is the target frequency, and the modulation 26 of the beat Mod is stronger in the deep region than in the shallow region. The equation for beat modulation is given by…”

“…An attempt to consider many electrodes has been made to optimize deep stimulation by using additional neck part electrodes in the international 10-10 system 26 . This is a method of optimizing in a sequential quadratic programming method 27 , with many constraints on the solution space consisting of each electrode current.…”