Transcranial focused ultrasound stimulation in the infralimbic cortex facilitates extinction of conditioned fear in rats
Jaeyong Lee, Ye Eun Kim, Jihong Lim, Yehhyun Jo, Hyunjoo Jenny Lee, Yong Sang Jo, June-Seek Choi
Brain Stimulation 2024 · 10.1016/j.brs.2024.03.013
Abstract
Transcranial focused ultrasound (tFUS) neuromodulation emerges as a promising non-invasive approach for improving neurological conditions. Extinction of conditioned fear has served as a prime model for exposure-based therapies for anxiety disorders. We investigated whether tFUS stimulation to a critical brain area, the infralimbic subdivision of the prefrontal cortex (IL), could facilitate fear extinction using rats. In a series of experiments, tFUS was delivered to the IL of a freely-moving rat and compared to sham stimulation (tFUS vs. SHAM). Initially, Fos expression in the IL was measured shortly after the stimulation. The results show that Fos expression was significantly increased in the IL but not in the neighboring regions compared to SHAM. Subsequently, two groups of rats were subjected to fear conditioning, extinction, and retention while receiving stimulation during the extinction. Rats in the tFUS group froze significantly less than SHAM during both extinction and retention tests. Importantly, the reduced freezing in the tFUS group was not attributable to non-specific effect such as auditory noise, as both groups demonstrated a similar level of locomotive activity in an open field regardless of the stimulation condition. Finally, we replicated the procedure with a shortened conditioning-to-extinction interval (15 min) to induce immediate extinction deficit. The tFUS group showed a facilitated reduction in freezing during the extinction, which persisted in the subsequent retention session compared to SHAM. In summary, the current findings suggest that tFUS stimulation in the IL facilitates fear extinction, offering a potential therapeutic regimen for fear-related psychiatric disorders.
Abstract via europepmc.
Exposures
Exposure 1: tFUS to the infralimbic cortex (5 MHz head-mounted stimulator)
Target: ventromedial prefrontal cortex — “the infralimbic subdivision of the prefrontal cortex (IL)”
Device: custom-built · Piezoelements, China (PZT disk); head-mounted stimulator fabricated in-house · head-mounted ultrasound stimulator (HMUS), PZT H4P85000 ✓
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 5,000 | ✓✓✓ |
| Pulse duration (ms) | 0.5 | ✓✓✓ |
| Pulse repetition frequency (Hz) | 1,000 | ✓✓✓ |
| Duty cycle (%) | not reportedpulse duration × PRF gives 50% | ⚑ |
| Sonication duration (s) | 30 | ✓✓✓⚑ |
| 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) | not reported | |
| In-situ Isppa (W/cm²) | 1.53 | ✓✓✓⚑ |
| In-situ Ispta (W/cm²) | not reported |
Pulsed sine waves (0.5 ms pulses at 1 kHz PRF) gated into bursts of 0.5 s with a 4.5 s inter-burst interval, total sonication 30 s per stimulation; applied concurrently with the CS during extinction (8 trials, or 20 in the immediate extinction experiment).
Flags from extraction
n_subjects— 61 rats across Experiments 1-3 (17, 22, 22 analysed groups); some rats were also used in the open field test.exposures[0].in_situ.isppa_w_cm2— Intensity measured in a soybean oil tank through an ex vivo rat skull; classed in_situ measurement. No pressure or ISPTA given.exposures[0].timing.sonication_duration_s— Total sonication duration of 30 s is built from 0.5 s bursts every 5 s (burst = a 0.5 s train of 0.5 ms pulses at 1 kHz); duty cycle not stated, not computed.exposures[0].timing.duty_cycle_pct— Not stated; nested burst structure.blinding— Only the Fos cell counting is stated to be done by an experimenter blinded to condition; recorded as single.auditory_control— Sham reversed the PZT to control for auditory confounding; masking by the tone CS argued in the discussion; no direct measurement.conditions— Healthy rats given fear conditioning and extinction (model of anxiety/PTSD therapy), no disease induced.n_sessions_per_subject— Stimulation on the extinction day (and an open field test two weeks later); total sessions not stated as a single number.exposures[0].device.family— Head-mounted transducer assembled in-house from a PZT disk (Piezoelements, China) and a 3D-printed lens.