Parameter specific modulation of neuronal firing and extracellular action potential dynamics by transcranial focused ultrasound stimulation in rat motor cortex
Haorun Huang, Charlotte Smets, Liyi Chen, Myles Mc Laughlin
Brain Stimulation 2026, 19, 103145 · 10.1016/j.brs.2026.103145
Abstract
Background Transcranial focused ultrasound stimulation (TUS) has emerged as a promising tool for noninvasive neuromodulation. However, the specific effects of stimulation parameters on neural activity remain incompletely understood. Objective This study investigates how variations in TUS pulse repetition frequency (PRF) and pulse duration (PD) influence neural activity in the rat motor cortex. Methods In vivo extracellular recordings were performed in anesthetized rats using 32-channel silicon probes while TUS was applied over the motor cortex. We systematically varied PRF (25, 50, 500 and 2000 Hz) and PD (50, 100, 200, 400 and 800 μs) and quantified changes in spike rate and extracellular action potential (EAP) shape. Control experiments included sonication of the visual cortex (V1) and the electrode holding bar. Effects were analyzed using linear mixed-effects models with Bonferroni-corrected post hoc testing. Results TUS caused a significant increase in spike rate at 500 Hz PRF when the PD was set at 200 μs. When PRF was set at 50 Hz, spike rate increase at 800 μs was significantly higher than at 50 μs and 100 μs. Analysis of the EAP revealed small but significant parameter-dependent changes in action potential shape. When the most effective excitatory parameters (500 Hz PRF, 800 μs PD) were combined, a larger spike rate increase was observed in the motor cortex, compared with the other tested PRF-PD combinations and a significant change in EAP shape. The same parameters applied in the control conditions caused a smaller spike rate increase in V1 but no significant effect with the bar control, and no EAP changes were detected. Conclusion These findings offer direct single-unit evidence that TUS can modify spike rate and is associated with subtle shifts in EAP waveform features in a parameter-dependent and region-specific manner. Optimizing PRF and PD is essential for reproducible neuromodulation and for moving TUS toward translational applications.
Abstract via europepmc.
Exposures
Exposure 1: Motor cortex PRF and PD sweeps (plus V1 and holding-bar controls)
Target: motor cortex — “rat motor cortex (AP 0.48 mm, ML 3.5 mm)”
Device: Ultran · Ultran Group Inc. · GS500-D13-P25 ✓
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 500 | ✓✓✓ |
| Pulse duration (ms) | 0.05, 0.1, 0.2, 0.4, 0.8swept | ✓✓✓ |
| Pulse repetition frequency (Hz) | 25, 50, 500, 2,000swept | ✓✓✓⚑ |
| Duty cycle (%) | not reported | ⚑ |
| Sonication duration (s) | 0.5 | ✓✓✓⚑ |
| Free-field pressure (kPa) | 1,320 | ✓✓✓⚑ |
|---|---|---|
| Free-field Isppa (W/cm²) | 58.1 | ✓✓✓ |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | not reported | |
| In-situ pressure (kPa) | not reported | |
| In-situ Isppa (W/cm²) | not reported | |
| In-situ Ispta (W/cm²) | not reported |
500 ms pulse trains once per second for a 3-min stimulation epoch, with 3-min pre and post epochs; PRF 25, 50, 500, 2000 Hz at fixed 200 us PD, and PD 50 to 800 us at fixed 50 Hz PRF; controls used 500 Hz and 800 us over V1 or the electrode holding bar.
Flags from extraction
n_subjects— 26 rats stated in methods, but 21 rats (PRF/PD sweeps) plus a separate cohort of 8 rats (controls) would give 29; 26 recorded as stated.exposures[0].timing.duty_cycle_pct— Duty cycle is never stated as a number (only discussed as derived from PRF and PD); left not_reported.exposures[0].timing.pulse_repetition_frequency_hz— PRF swept 25-2000 Hz at fixed 200 us PD; PD swept 50-800 us at fixed 50 Hz PRF; the control cohort used 500 Hz and 800 us.exposures[0].free_field.pressure_kpa— 1.32 MPa measured in a water tank calibration (hydrophone, no skull); recorded as free field. Not stated whether it is peak negative or peak.exposures[0].timing.sonication_duration_s— 500 ms pulse trains delivered once per second for a 3-min stimulation epoch.exposures[0].in_situ— No in-situ (through skull or brain) value is reported.