Transcranial Ultrasound Stimulation Unravels the Causal Role of the Left Inferior Frontal Gyrus in Syntactic Processing
harry-luyao Chen, Guang Yang, Xingfang Qu, Dongwei Li, Chenguang Zhao, Junjie Wu, Ke Zeng, Yifei He, Gesa Hartwigsen, Robert Chen, Angela D. Friederici
2026 · 10.21203/rs.3.rs-8717654/v1
Abstract
Hierarchical syntactic processing is a fundamental ability for human language processing. Previous studies dispute the left inferior frontal gyrus (LIFG) and the left posterior temporal lobe (LpTL as its possible neural underpinnings, however, direct comparisons of the role of these regions during sentence comprehension are rare. We are among the first to use transcranial ultrasound stimulation (TUS), a non-invasive brain stimulation technique with high precision, to test the causal roles of the different brain regions in processing complex sentences (with embedded relative clauses) and simpler coordinated sentences. Participants completed three lab visits (7 days apart), with LIFG, LpTL, or vertex (control) stimulated each time. Our TUS experiment provides consistent evidence for a causal role of the LIFG in syntactic processing: LIFG TUS significantly decreased d-prime (d’) sensitivity, prolonged reaction times (RTs), and impaired evidence accumulation during decision-making revealed by the hierarchical drift-diffusion modeling. Our findings besides demonstrating the TUS efficacy in sentence-level syntactic processing strengthen the crucial role of LIFG (not LpTL) for hierarchical syntactic processing, thereby deepen the understanding of this core language faculty’s causal neural mechanisms.
Abstract via europepmc.
Exposures
Exposure 1: LIFG tbTUS
Target: inferior frontal gyrus — “left inferior frontal gyrus (LIFG), EEG site F7”
Device: other named manufacturer · Jiangxi Jielian Medical Equipment Co., Ltd. · JL-TUS-200 ✓
| Waveform | theta burst | |
|---|---|---|
| Fundamental frequency (kHz) | 500 | ✓✓✓ |
| Pulse duration (ms) | 20 | ✓✓✓ |
| Pulse repetition frequency (Hz) | 5 | ✓✓✓⚑ |
| Duty cycle (%) | not reportedpulse duration × PRF gives 10% | ⚑ |
| Sonication duration (s) | 80 | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | 9.67 | ✓✓✓⚑ |
| Free-field Ispta (W/cm²) | 1.73 | ✓✓✓ |
| 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 |
tbTUS protocol defined as an 80 s train of 20 ms ultrasound pulses repeated every 200 ms, delivered offline before the sentence task; targeted via EEG site F7.
Exposure 2: LpTL tbTUS
Target: temporal lobe — “left posterior temporal lobe (LpTL), EEG site TP7”
Device: other named manufacturer · Jiangxi Jielian Medical Equipment Co., Ltd. · JL-TUS-200 ✓
| Waveform | theta burst | |
|---|---|---|
| Fundamental frequency (kHz) | 500 | ✓✓✓ |
| Pulse duration (ms) | 20 | ✓✓✓ |
| Pulse repetition frequency (Hz) | 5 | ✓✓✓ |
| Duty cycle (%) | not reportedpulse duration × PRF gives 10% | |
| Sonication duration (s) | 80 | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | 9.67 | ✓✓✓ |
| Free-field Ispta (W/cm²) | 1.73 | ✓✓✓ |
| 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 |
tbTUS protocol defined as an 80 s train of 20 ms ultrasound pulses repeated every 200 ms, delivered offline before the sentence task; targeted via EEG site TP7.
Exposure 3: Vertex tbTUS (active control)
Target: cerebral cortex — “vertex (Cz)”
Device: other named manufacturer · Jiangxi Jielian Medical Equipment Co., Ltd. · JL-TUS-200 ✓
| Waveform | theta burst | |
|---|---|---|
| Fundamental frequency (kHz) | 500 | ✓✓✓ |
| Pulse duration (ms) | 20 | ✓✓✓ |
| Pulse repetition frequency (Hz) | 5 | ✓✓✓ |
| Duty cycle (%) | not reportedpulse duration × PRF gives 10% | |
| Sonication duration (s) | 80 | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | 9.67 | ✓✓✓ |
| Free-field Ispta (W/cm²) | 1.73 | ✓✓✓ |
| 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 |
tbTUS protocol defined as an 80 s train of 20 ms ultrasound pulses repeated every 200 ms, delivered offline before the sentence task; targeted via EEG site Cz as active control.
Flags from extraction
exposures[0].in_situ.isppa_w_cm2— Paper says Isppa and Ispta dropped by approximately fivefold after a human skull but gives no in situ value; recorded as not_reported.exposures[0].timing.duty_cycle_pct— Not stated; not computed.exposures[0].timing.pulse_repetition_frequency_hz— Converted from 'repeated every 200 ms'.exposures[0].timing.waveform— Paper calls the protocol tbTUS but describes it as 20 ms pulses every 200 ms for 80 s, i.e. a single-level 5 Hz train.exposures[0].free_field.isppa_w_cm2— Free-water values come from a previous characterisation study of the transducer, quoted here.randomised— Session order described as balanced across participants; randomisation not stated.exposures[2].target.terms— Vertex has no specific term; mapped to cerebral_cortex.