Neuromodulatory Responses Elicited by Intermittent versus Continuous Transcranial Focused Ultrasound Stimulation of the Motor Cortex in Rats
Tsung-Hsun Hsieh, Po-Chun Chu, Thi Xuan Dieu Nguyen, Chi-Wei Kuo, Pi-Kai Chang, Kai-Hsiang Stanley Chen, Hao-Li Liu
International Journal of Molecular Sciences 2024, 25, 5687 · 10.3390/ijms25115687
Abstract
Transcranial focused ultrasound stimulation (tFUS) has emerged as a promising neuromodulation technique that delivers acoustic energy with high spatial resolution for inducing long-term potentiation (LTP)- or depression (LTD)-like plasticity. The variability in the primary effects of tFUS-induced plasticity could be due to different stimulation patterns, such as intermittent versus continuous, and is an aspect that requires further detailed exploration. In this study, we developed a platform to evaluate the neuromodulatory effects of intermittent and continuous tFUS on motor cortical plasticity before and after tFUS application. Three groups of rats were exposed to either intermittent, continuous, or sham tFUS. We analyzed the neuromodulatory effects on motor cortical excitability by examining changes in motor-evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS). We also investigated the effects of different stimulation patterns on excitatory and inhibitory neural biomarkers, examining c-Fos and glutamic acid decarboxylase (GAD-65) expression using immunohistochemistry staining. Additionally, we evaluated the safety of tFUS by analyzing glial fibrillary acidic protein (GFAP) expression. The current results indicated that intermittent tFUS produced a facilitation effect on motor excitability, while continuous tFUS significantly inhibited motor excitability. Furthermore, neither tFUS approach caused injury to the stimulation sites in rats. Immunohistochemistry staining revealed increased c-Fos and decreased GAD-65 expression following intermittent tFUS. Conversely, continuous tFUS downregulated c-Fos and upregulated GAD-65 expression. In conclusion, our findings demonstrate that both intermittent and continuous tFUS effectively modulate cortical excitability. The neuromodulatory effects may result from the activation or deactivation of cortical neurons following tFUS intervention. These effects are considered safe and well-tolerated, highlighting the potential for using different patterns of tFUS in future clinical neuromodulatory applications.
Abstract via europepmc.
Exposures
Exposure 1: Intermittent vs continuous tFUS to right primary motor cortex
Target: primary motor cortex — “right primary motor cortex”
Device: other named manufacturer · NepaGene · SonoPore KTAC-4000 ✓
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 1,000 | ✓✓✓ |
| Pulse duration (ms) | not reported | ⚑ |
| Pulse repetition frequency (Hz) | not reported | |
| Duty cycle (%) | 30, 8swept | ✓✓✓ |
| Sonication duration (s) | 30, 600swept | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | measurementsingle value | |
| In-situ pressure (kPa) | 137 | ✓✓✓ |
| In-situ Isppa (W/cm²) | not reported | |
| In-situ Ispta (W/cm²) | 0.188, 0.0469swept | ✓✓✓⚑ |
Intermittent transcranial tFUS: 30 s ultrasound trains (30% duty cycle) followed by 90 s rest periods, repeated five times for a total duration of 600 s. Continuous tFUS: same pressure at an 8% duty cycle for a continuous duration of 600 s. Both delivered as a single 600 s intervention under anaesthesia.
Flags from extraction
n_subjects— Group sizes (7-8 rats per group) are stated only in the Figure 1 legend, not in main text or a table, so per the three-way rule this is recorded as not_reported.exposures[0].in_situ.ispta_w_cm2— List order is [intermittent, continuous] matching duty_cycle_pct and sonication_duration_s list order.exposures[0].timing.pulse_duration_ms— No pulse repetition frequency or intra-train pulse duration is stated, only the overall duty cycle of each protocol, so the burst rule cannot be resolved; both durations (30 s train and 600 s continuous) are given in protocol_description.exposures[0]— Intermittent and continuous protocols are treated as one exposure (same target and frequency) with timing parameters as lists, per the one-exposure-per-target-frequency rule.