Low-Intensity Ultrasound Causes Direct Excitation of Auditory Cortical Neurons
Xiaofei Qi, Kexin Lyu, Long Meng, Cuixian Li, Hongzheng Zhang, Lili Niu, Zhengrong Lin, Hairong Zheng, Jie Tang
Neural Plasticity 2021 · 10.1155/2021/8855055
Abstract
Cochlear implantation is the first-line treatment for severe and profound hearing loss in children and adults. However, deaf patients with cochlear malformations or with cochlear nerve deficiencies are ineligible for cochlear implants. Meanwhile, the limited spatial selectivity and high risk of invasive craniotomy restrict the wide application of auditory brainstem implants. A noninvasive alternative strategy for safe and effective neuronal stimulation is urgently needed to address this issue. Because of its advantage in neural modulation over electrical stimulation, low-intensity ultrasound (US) is considered a safe modality for eliciting neural activity in the central auditory system. Although the neural modulation ability of low-intensity US has been demonstrated in the human primary somatosensory cortex and primary visual cortex, whether low-intensity US can directly activate auditory cortical neurons is still a topic of debate. To clarify the direct effects on auditory neurons, in the present study, we employed low-intensity US to stimulate auditory cortical neurons in vitro. Our data show that both low-frequency (0.8 MHz) and high-frequency (>27 MHz) US stimulation can elicit the inward current and action potentials in cultured neurons. c-Fos staining results indicate that low-intensity US is efficient for stimulating most neurons. Our study suggests that low-intensity US can excite auditory cortical neurons directly, implying that US-induced neural modulation can be a potential approach for activating the auditory cortex of deaf patients.
Abstract via crossref.
Exposures
Exposure 1: Focused low-frequency ultrasound (tone burst pulses) to cultured auditory cortical neurons
Target: cultured neurons — “cultured auditory cortical neurons (primary culture from mouse auditory cortex)”
Device: custom-built
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 800 | ✓✓✓ |
| Pulse duration (ms) | not reportedimplied by duty cycle ÷ PRF: 0.5 ms (not stated by the paper) | ⚑ |
| Pulse repetition frequency (Hz) | 1,000 | ✓✓✓ |
| Duty cycle (%) | 50 | ✓✓✓ |
| Sonication duration (s) | not reported | ⚑ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | not applicable | |
| In-situ pressure (kPa) | not applicable | |
| In-situ Isppa (W/cm²) | not applicable | |
| In-situ Ispta (W/cm²) | not applicable | |
| Pressure, domain unspecified (kPa) | 300 | ✓✓✓⚑ |
Each US stimulation contains 500 tone burst pulses at a center frequency of 0.8 MHz and a repetition frequency of 1 kHz with a duty cycle of 50%. The interval between stimulus was 1 second. During recordings, US stimulation was delivered to the recorded cell every other second for 20 s (HEK293T control experiment); for cortical neurons, responses to the same 500-pulse stimulus were compared before and during US delivery.
Exposure 2: High-frequency surface acoustic wave (SAW) chip stimulation of cultured auditory cortical neurons
Target: cultured neurons — “cultured auditory cortical neurons on SAW chip”
Device: custom-built
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 27,420 | ✓✓✓ |
| Pulse duration (ms) | not reported | |
| Pulse repetition frequency (Hz) | not reported | ⚑ |
| Duty cycle (%) | not reported | |
| Sonication duration (s) | 1 | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | not applicable | |
| In-situ pressure (kPa) | not applicable | |
| In-situ Isppa (W/cm²) | not applicable | |
| In-situ Ispta (W/cm²) | not applicable | |
| Pressure, domain unspecified (kPa) | 130 | ✓✓✓⚑ |
A custom-made ultrasound neuromodulation chip (interdigital transducers plus agar plate) generated surface acoustic waves at a resonant frequency of 27.42 MHz. Cells cultured on slips received US stimulation for 1 s with a 9 s interval; for the c-Fos experiment, cells were fixed within 30 min after 5 min of cumulative US stimulation, and for action-potential recordings the firing rate was measured after 15 rounds of stimulation.
Consistency checks: f0 out of range.
Flags from extraction
n_subjects— This is a cell-culture electrophysiology study (n counted per neuron/recording, e.g. n=6, n=7, n=9 across different sub-experiments); no single subject/culture count applies, so n_subjects/n_sessions_per_subject/randomised/blinding are left null as not applicable to this preparation type.exposures[0].timing.pulse_duration_ms— Pulse duration is not explicitly stated; it could be computed from duty cycle (50%) and PRF (1 kHz) as 0.5 ms, but the paper does not state this directly, so it is left not_reported per the no-arithmetic rule.exposures[0].timing.sonication_duration_s— The single-train duration (500 pulses at 1 kHz PRF) is not explicitly stated in seconds; it could be computed as ~0.5 s from pulse count and PRF but this would be arithmetic not stated by the authors.exposures[1].timing.pulse_repetition_frequency_hz— The paper states 'the ultrasound frequency, RPF, and voltage amplitude were controlled' for the SAW chip but never gives the numeric repetition frequency value used.exposures[0].unspecified_domain.pressure_kpa— Domain not stated (dish/bath preparation, pressure measured 'peak-to-peak' without specifying free-field vs at-cell location); placed in unspecified_domain.exposures[1].unspecified_domain.pressure_kpa— Domain not stated; pressure was measured by laser Doppler velocimetry of the chip surface, not explicitly labelled free-field or in-situ; placed in unspecified_domain.