Effects of hippocampal noninvasive theta-burst stimulation on consolidation of associative memory in healthy older adults

Abstract

Stimulation of deep brain areas can offer benefits against cognitive impairments associated with aging. So far, this was only possible via invasive methods accompanied by risks. Grossman et al. proposed a new noninvasive stimulation technique, transcranial temporal interference electric stimulation (tTIS), which can be steered to target and modulate activity of deep brain structures. Memory capacity depends on subcortical structures such as the hippocampus, hence, modulation of hippocampal activity could benefit declining cognitive functions. The current study investigates whether theta-burst patterned tTIS targeting the hippocampus influences performance of associative memory in older adults. We found that theta-burst patterned tTIS, but not the control stimulation, improved recollection time in a follow-up 24h after the stimulation, suggesting that theta-burst patterned tTIS can influence the efficiency of longer-term encoding. This outcome indicates that tTIS may provide a new noninvasive deep brain stimulation method to modulate senescent memory processes.

Electric field temporal interference stimulation of neurons in vitro

“…This result is also in line with a previous in vivo study that reported hippocampal TIS to improve associative memory 24 hours after stimulation, but not earlier, after 90 minutes (Δf = 5 Hz). 11 Burst durations, spikes in bursts, BSRs, and ISI in bursts remained unchanged for all the stimulation conditions 24 hours after the stimulation (Fig. 6C-F and H).…”

“…6 TIS has been reported to cause minimal side effects and high tolerability. [7][8][9][10] Previously, TIS at theta or gamma frequency envelopes has been used to modulate brain activity in the hippocampus, 6,8,11 striatum, 8,12 and motor cortex, 7,9 demonstrating a targeted stimulation with minimal exposure to overlying brain areas. 6,12 Specifically, theta-frequency TIS has been shown to modulate hippocampal activity, enhance memory performance, 6,11 and alter functional connectivity after TIS.…”

“…[7][8][9][10] Previously, TIS at theta or gamma frequency envelopes has been used to modulate brain activity in the hippocampus, 6,8,11 striatum, 8,12 and motor cortex, 7,9 demonstrating a targeted stimulation with minimal exposure to overlying brain areas. 6,12 Specifically, theta-frequency TIS has been shown to modulate hippocampal activity, enhance memory performance, 6,11 and alter functional connectivity after TIS. 6 When targeted to the striatum, TIS has been shown to improve motor performance, and modulate the activity in the targeted structures.…”

“…Control values (before stimulation) were adjusted to 0, indicating no change. Values below 0 show decreases and values above 0 show increases in the respective activity parameters compared to control cultures (n = 4 MEAs/condition; Mann-Whitney U test; ns = not significant, *p = 0.0286) that have been applied in vivo 6,[8][9][10][11][12]. Due to present hardware limitations, we were not able to replicate the Grossman setup 1 with respect to the carrier frequency.…”