How do mice react to ultrasonic sound? - briefly
Mice detect frequencies above 20 kHz and usually display startle, freezing, or avoidance reactions, occasionally emitting ultrasonic vocalizations. These behaviors are driven by cochlear hair cells specialized for high‑frequency hearing.
How do mice react to ultrasonic sound? - in detail
Mice possess an auditory system tuned to frequencies far above the human hearing range, typically 20–100 kHz. When exposed to ultrasonic tones, they exhibit a cascade of measurable reactions that can be grouped into behavioral, physiological, and neural categories.
Behavioral responses appear within milliseconds of stimulus onset. Common actions include:
- Rapid orientation of the head toward the source, indicating sound localization.
- Short bursts of locomotion, often a series of quick sprints or jumps, termed “startle” or “escape” runs.
- Freezing or immobility when the tone is presented at low intensities, suggesting a threat assessment.
- Repetitive grooming or sniffing when the sound is sustained, reflecting exploratory or investigative behavior.
The magnitude and pattern of these actions depend on frequency and sound pressure level. Frequencies between 30 and 50 kHz at moderate intensities (60–70 dB SPL) most frequently trigger startle responses, while higher frequencies (>80 kHz) at comparable intensities tend to induce freezing. Repeated exposure leads to habituation; the same tone presented over several trials reduces both locomotor bursts and freezing duration, indicating learning and sensory adaptation.
Physiological changes accompany the overt behavior. Heart rate accelerates during startle episodes, measurable by telemetry implants or surface electrodes. Corticosterone concentrations rise in blood samples collected shortly after exposure, confirming activation of the hypothalamic‑pituitary‑adrenal axis. Pupillary dilation, recorded with infrared cameras, correlates with arousal level and intensity of the stimulus.
Neural recordings reveal the underlying circuitry. Auditory brainstem nuclei, especially the inferior colliculus, show increased firing rates that scale with frequency and amplitude. In the auditory cortex, multi‑unit activity displays precise temporal locking to the ultrasonic waveform, while the amygdala exhibits heightened activation during aversive tones, linking auditory input to emotional processing. Optogenetic inhibition of the medial geniculate body attenuates both startle and freezing, demonstrating its pivotal role in transmitting ultrasonic information to higher centers.
Experimental paradigms vary. Free‑field speakers calibrated with a probe microphone deliver controlled tones, while ultrasonic playback cages allow continuous monitoring of movement via video tracking software. Electrophysiological studies often employ anesthetized preparations to isolate peripheral responses, whereas awake, head‑fixed mice provide data on cortical processing without confounding motor artifacts.
Species and strain differences influence sensitivity. Laboratory strains such as C57BL/6J display lower thresholds for startle than wild‑derived Mus musculus subspecies, possibly due to genetic variations in hair cell function. Age also matters: juvenile mice (<4 weeks) respond more vigorously, whereas adults (>12 weeks) show reduced amplitude in both behavioral and neural metrics.
In summary, ultrasonic exposure elicits rapid orientation, escape, freezing, and investigative behaviors, accompanied by cardiovascular, hormonal, and neural activation. The precise pattern of reaction is shaped by acoustic parameters, prior experience, genetic background, and developmental stage.