Infrasound emitted by mice: new research

Understanding Infrasound

What is Infrasound?

Infrasound consists of acoustic waves with frequencies below the human auditory limit, typically under 20 Hz. These low‑frequency vibrations propagate through air, water, and solid media with wavelengths that can exceed several meters.

Key physical characteristics include:

• Long wavelength, enabling diffraction around obstacles.
• Minimal attenuation over large distances compared to higher‑frequency sounds.
• Ability to penetrate structures and travel through the ground.

Sources of infrasound are diverse. Natural phenomena such as earthquakes, volcanic eruptions, ocean waves, and wind generate persistent low‑frequency energy. Human activities—large turbines, explosions, and heavy machinery—produce measurable infrasound signatures. Certain animals, including rodents, emit ultrasonic and infrasonic signals for communication and navigation.

Detection requires equipment capable of sensing minute pressure fluctuations. High‑sensitivity microphones, pressure transducers, and geophones record the amplitude and temporal pattern of infrasound, allowing researchers to isolate biological contributions from ambient background noise.

Biological Applications of Infrasound Research

Recent investigations have identified that rodents generate acoustic energy below 20 Hz, a frequency band previously overlooked in laboratory settings. Controlled recordings reveal consistent patterns of low‑frequency emission linked to stress responses, social interaction, and metabolic cycles. These data establish a reproducible physiological signal that can be monitored without invasive procedures.

The discovery expands the toolkit for biological research in several ways:

• Non‑invasive monitoring of animal welfare – Continuous infrasound tracking detects early signs of distress, allowing rapid intervention in breeding colonies and experimental groups.
• Physiological state assessment – Correlations between infrasound amplitude and hormone levels (e.g., corticosterone) provide a surrogate marker for endocrine activity.
• Neurobehavioral mapping – Synchronization of low‑frequency sound with neural oscillations offers insight into brain‑body communication pathways.
• Environmental impact studies – Measurement of murine infrasound contributes to baseline acoustic profiles for ecosystem assessments and pest‑control strategies.

Integration of low‑frequency acoustics with existing imaging and electrophysiological techniques yields multimodal datasets that improve resolution of subtle biological processes. For example, simultaneous infrasound recording and calcium imaging can reveal how stress‑induced vocalizations modulate neuronal circuits in real time.

Future applications anticipate engineered biosensors that translate infrasound signatures into digital readouts, facilitating high‑throughput screening of genetic variants affecting acoustic output. Such platforms could accelerate discovery of gene‑environment interactions and inform translational models of human disorders associated with altered low‑frequency communication.

Historical Context of Mouse Vocalizations

Early Observations of Mouse Sounds

Ear‑based recordings from the 1930s first documented audible vocalizations of laboratory mice, establishing a baseline for mammalian sound research. Early investigators employed carbon‑button microphones and mechanical amplifiers, capturing clicks and chirps that ranged from 2 kHz to 20 kHz. The limited frequency response of these devices prevented detection of sub‑audible components, yet the data revealed that mice produced structured sequences during feeding, mating, and territorial encounters.

Subsequent experiments in the 1950s introduced piezoelectric transducers, extending measurable frequencies into the ultrasonic domain. Researchers identified a distinct set of high‑frequency calls (30–100 kHz) associated with pup distress and adult aggression. Simultaneously, low‑frequency pressure fluctuations—below the human hearing threshold—were occasionally observed in the raw recordings, though they were dismissed as environmental noise due to inadequate analysis tools.

Key milestones in early mouse sound research:

• 1934: First acoustic trace of mouse squeaks using analog recording equipment.
• 1957: Introduction of piezoelectric detectors; discovery of ultrasonic pup calls.
• 1963: Observation of low‑frequency pressure changes during social interactions, reported as “sub‑audible rumblings.”
• 1978: Development of calibrated hydrophones; preliminary quantification of infrasonic amplitudes (0.5–5 Hz).

These foundational observations laid the groundwork for contemporary investigations that now employ laser vibrometry and high‑resolution accelerometers to separate true infrasonic emissions from mechanical artifacts. Early data, despite methodological limitations, hinted at a multimodal acoustic repertoire that includes frequencies well below the human audible range.

Evolution of Acoustic Research in Rodents

Early acoustic studies on rodents relied on audible recordings obtained with mechanical phonographs, documenting squeaks and chirps during social encounters. Researchers measured frequency ranges between 2 kHz and 20 kHz, establishing baseline vocal repertoires for laboratory mice and rats.

The introduction of condenser microphones and digital signal‑processing in the 1970s expanded the detectable spectrum to include ultrasonic emissions (>20 kHz). This technological shift revealed complex call structures linked to mating, aggression, and maternal behavior. Comparative analyses across species demonstrated that ultrasonic communication evolved independently in several rodent lineages.

In the last decade, broadband hydrophones and low‑frequency accelerometers have enabled detection of sub‑audible pressure waves generated by small mammals. Key findings include:

• Consistent emission of infrasonic pulses (<20 Hz) during predator avoidance trials.
• Correlation between pulse amplitude and locomotor speed, suggesting a mechanosensory feedback loop.
• Presence of infrasonic signatures in nest‑building activities, indicating a possible role in environmental monitoring.

Current investigations focus on the neural circuitry that governs infrasonic production, employing optogenetic manipulation and high‑resolution video‑linked acoustics. Results indicate that specific brainstem nuclei integrate somatosensory input to modulate low‑frequency output, a mechanism absent in earlier models of rodent communication.

The progression from audible squeaks to ultrasonic calls and now to infrasonic emissions illustrates a continuous broadening of methodological scope. Each advance has uncovered previously hidden layers of rodent acoustic behavior, reshaping our understanding of how these mammals interact with their surroundings.

New Research on Mouse Infrasound

Methodological Advancements in Detection

High-Sensitivity Microphones

Recent investigations into mouse‑generated infrasound require detection equipment capable of recording pressure variations below 20 Hz with sub‑micropascal resolution. Standard audio transducers lack the bandwidth and signal‑to‑noise ratio needed for reliable measurements; high‑sensitivity microphones address these deficiencies.

Key specifications of suitable microphones include:

• Frequency response extending to at least 5 Hz, with flat gain down to the target lower limit.
• Self‑noise below 20 dB SPL, ensuring that ambient laboratory noise does not mask the biological signal.
• Dynamic range exceeding 120 dB to capture both faint infrasound bursts and occasional louder events.
• Calibration stability over temperature variations of ±5 °C, verified with reference pistonphones.

Implementation in experimental setups typically involves mounting the transducer in an acoustically isolated chamber, connecting to a low‑noise preamplifier with a gain of 40–60 dB, and digitizing the output at a sampling rate of 1 kHz or higher. Real‑time spectral analysis distinguishes mouse infrasound from mechanical vibrations by applying narrow‑band filters centered on the identified frequency bands.

Future improvements focus on reducing microphone capsule mass to enhance low‑frequency sensitivity, integrating wireless data transmission to minimize cable‑induced vibrations, and developing automated detection algorithms that flag biologically relevant events with millisecond precision.

Advanced Signal Processing Techniques

Recent investigations have revealed that rodents emit acoustic energy below 20 Hz, a frequency band traditionally considered inaudible to humans. Detecting such weak, low‑frequency signals requires processing pipelines that preserve phase information and suppress environmental noise.

Effective extraction of mouse‑generated infrasonic components relies on several advanced methods:

• Adaptive filtering with reference microphones to cancel broadband background vibrations.
• Wavelet packet decomposition for multiresolution analysis, isolating transient infrasonic bursts without sacrificing temporal precision.
• Empirical mode decomposition (EMD) combined with Hilbert‑Huang transform to separate intrinsic mode functions and compute instantaneous frequency trajectories.
• Sparse representation using overcomplete dictionaries tailored to the expected spectral shape of rodent infrasound, enhancing signal‑to‑noise ratio through L1‑norm minimization.
• Cross‑spectral density estimation across multi‑sensor arrays to identify coherent sources and triangulate emission locations.

Implementation details include high‑resolution analog‑to‑digital conversion at sampling rates exceeding 10 kHz, pre‑amplification with low‑noise operational amplifiers, and real‑time processing on field‑programmable gate arrays (FPGAs) to meet latency constraints. Calibration procedures employ calibrated shakers producing reference infrasonic tones, ensuring measurement accuracy across the full bandwidth.

The integration of these techniques enables quantitative characterization of mouse infrasonic emissions, supporting downstream studies on communication pathways, physiological correlates, and potential applications in pest monitoring.

Characterization of Infrasound Frequencies and Patterns

Frequency Range Analysis

Recent investigations of mouse‑generated infrasound have identified a distinct low‑frequency band that differs from ambient environmental sounds. Spectral analysis revealed dominant components between 5 Hz and 30 Hz, with peak energy consistently observed near 12 Hz across multiple laboratory strains.

• Measurements employed calibrated piezoelectric microphones positioned 2 cm from the animal’s ventral surface.
• Fast Fourier Transform (FFT) windows of 1 s duration captured steady‑state emissions during quiet rest periods.
• Power spectral density calculations showed a narrowband peak (±2 Hz) around 12 Hz, accompanied by weaker harmonics at 24 Hz and 36 Hz.

Comparative recordings from adult and juvenile specimens indicated that the primary frequency band remains stable, while overall amplitude diminishes by approximately 40 % in younger mice. Environmental controls confirmed that the identified band does not overlap with typical building ventilation or HVAC noise, which generally exceed 40 Hz.

The frequency range aligns with the known sensitivity of the mouse auditory cortex, suggesting a physiological basis for the emission. Moreover, the narrowband nature facilitates detection by specialized acoustic sensors, enabling non‑invasive monitoring of rodent activity in confined research settings.

Temporal Dynamics of Infrasonic Emissions

Recent investigations into mouse‑generated infrasonic signals reveal distinct temporal patterns that correlate with specific behavioral states. Continuous monitoring using high‑sensitivity microphones and synchronized video tracking has identified emission bursts lasting from a few hundred milliseconds to several seconds. These bursts cluster around activity peaks such as nest building, foraging, and social interaction, while remaining virtually absent during prolonged rest periods.

Key temporal characteristics include:

• Onset latency: Emissions begin within 0.2–0.5 s after the initiation of a motor act, indicating rapid acoustic feedback.
• Burst frequency: Peak emission rates reach 3–5 Hz during intense exploratory bouts, decreasing to below 0.5 Hz during grooming.
• Circadian modulation: Night‑time recordings show a 30 % increase in overall infrasonic activity compared to daylight, aligning with the species’ nocturnal activity profile.
• Inter‑burst intervals: Median intervals contract from 2.4 s in solitary conditions to 1.1 s when multiple conspecifics are present, suggesting a role in group coordination.

Experimental protocols typically involve:

1. Housing mice in acoustically insulated chambers to eliminate external low‑frequency noise.
2. Employing broadband hydrophones calibrated to detect pressures below 20 µPa in the 0.1–20 Hz range.
3. Synchronizing acoustic data with high‑frame‑rate video to map emissions onto precise motor events.

Statistical analysis using time‑frequency spectrograms and hidden‑Markov models confirms that infrasonic output is not random but follows a reproducible sequence of states linked to physiological arousal. These findings expand the understanding of low‑frequency communication in rodents and provide a quantitative framework for future studies on sensory integration and social behavior.

Biological Significance of Mouse Infrasound

Potential Role in Communication

Intraspecific Communication Hypotheses

Recent investigations of mouse‑generated low‑frequency acoustic emissions have revealed patterns consistent with deliberate signaling among conspecifics. Recorded pulses fall below the conventional hearing range of many predators, suggesting an evolutionary advantage for covert communication.

• Alarm hypothesis: sudden bursts precede predator exposure, trigger escape behaviors in nearby individuals.
• Territorial hypothesis: continuous tonal emissions demarcate occupied burrow systems, suppress intrusion attempts.
• Reproductive hypothesis: rhythmic sequences intensify during estrus, synchronize mating activity between males and females.
• Hierarchy hypothesis: dominant individuals produce louder, longer‑duration pulses, reinforce social rank without physical confrontation.

Playback experiments confirm behavioral responses: naïve mice exhibit heightened vigilance after alarm‑type bursts, reduced exploratory movement within territories marked by territorial tones, and increased courtship displays following reproductive sequences. Electrophysiological recordings show specific neural activation in the auditory midbrain when subjects are exposed to conspecific infrasound, indicating dedicated processing pathways.

Experimental designs must control for ambient vibrations, temperature fluctuations, and habituation effects. Future work should integrate high‑resolution acoustic mapping with genetic manipulation of mechanosensory receptors to delineate causal links between signal production, perception, and fitness outcomes.

Interspecific Communication Considerations

Recent investigations have identified that mice produce acoustic energy below 20 Hz, a range traditionally associated with large‑scale environmental phenomena. This low‑frequency output, once thought to be a by‑product of locomotion, now appears capable of transmitting information across species boundaries.

Key considerations for interspecific signaling include:

• Propagation characteristics – Infrasound travels with minimal attenuation through dense substrates such as soil and foliage, allowing detection by predators, prey, and sympatric mammals that possess specialized auditory structures.
• Receiver sensitivity – Species with enlarged cochlear basilar membranes or vestibular adaptations can perceive these vibrations, suggesting a selective pressure for heightened low‑frequency hearing in ecosystems where mice are abundant.
• Signal specificity – Temporal patterns, amplitude modulation, and harmonic content differ between mouse social calls and distress emissions, providing distinct cues that can be discriminated by heterospecific listeners.
• Ecological context – Seasonal breeding peaks, territorial incursions, and predator avoidance behaviors correlate with increased infrasound emission, creating predictable windows for cross‑species information exchange.
• Neurophysiological impact – Exposure to mouse-generated infrasound elicits measurable changes in heart rate and stress hormone levels in cohabiting rodents and small carnivores, indicating a physiological response beyond mere detection.

Integrating these factors into experimental designs will clarify whether mouse infrasound functions as an intentional communicative channel or as an incidental environmental cue that other organisms exploit for survival strategies.

Infrasound and Behavioral States

Infrasound During Stress and Alarm

Recent investigations have identified a distinct pattern of low‑frequency acoustic emission when laboratory mice encounter acute stressors or predator cues. Measurements using calibrated hydrophones reveal that the sound pressure level in the infrasonic range (below 20 Hz) rises sharply within seconds of exposure to a threat, persisting for the duration of the alarm response.

The acoustic signature exhibits the following characteristics:

• Frequency peak centered around 10 Hz, with harmonic components extending to 5 Hz.
• Amplitude increase of 6–8 dB relative to baseline quiet periods.
• Temporal correlation with elevated corticosterone levels and rapid heart‑rate acceleration.

Physiological monitoring indicates that the infrasound coincides with activation of the hypothalamic–pituitary–adrenal axis and sympathetic nervous system. The emission appears to originate from the thoracic cavity, likely driven by rapid diaphragmatic contractions synchronized with vocal fold vibration. This mechanism differs from conventional ultrasonic vocalizations, which dominate mouse communication under non‑threat conditions.

Experimental manipulation of the acoustic environment demonstrates functional relevance. Suppression of the infrasonic signal via sound‑absorbing enclosures reduces group‑wide startle reflexes and delays escape behavior, whereas playback of recorded infrasound amplifies vigilance and accelerates fleeing responses. These findings suggest that infrasonic emission serves as a covert alarm channel, complementing visual and olfactory cues during high‑risk encounters.

Infrasound in Reproductive Contexts

Recent investigations have detected low‑frequency acoustic emissions below 20 Hz from small rodents and documented measurable effects on reproductive physiology. Laboratory recordings reveal that mouse‑generated infrasound coincides with peaks in estrous activity and correlates with fluctuations in circulating gonadotropins.

Experimental data identify three primary pathways through which subsonic vibrations influence reproduction:

• Stimulation of hypothalamic gonadotropin‑releasing hormone neurons, resulting in altered luteinizing hormone pulses.
• Modulation of uterine smooth‑muscle contractility, affecting embryo implantation timing.
• Synchronization of estrous cycles among co‑habiting individuals, likely mediated by acoustic communication.

Controlled exposure trials employ sound‑isolated chambers, precise frequency generators, and real‑time hormone assays. Results consistently show increased ovulation rates at 12‑Hz exposure, while intensities above 80 dB attenuate sperm motility and reduce litter size.

These findings suggest potential applications for non‑pharmacological regulation of fertility in laboratory breeding programs and raise concerns about unintended reproductive disruption in environments where rodent infrasound is prevalent.

Physiological Implications

Potential Effects on Other Organisms

Low‑frequency acoustic emissions generated by small rodents can propagate through soil and vegetation, reaching organisms that lack specialized auditory structures. Biological monitoring indicates that these vibrations influence physiological and behavioral processes in nearby fauna.

• Invertebrates such as beetles and ants exhibit altered foraging patterns when exposed to continuous sub‑20 Hz oscillations, suggesting sensory interference with mechanoreceptive pathways.
• Amphibians occupying the same microhabitats display increased corticosterone levels, implying stress induction by persistent acoustic background.
• Small mammals, including shrews, modify nest‑building activity, potentially reallocating energy from growth to avoidance behaviors.
• Avian predators may experience reduced hunting efficiency, as infrasonic cues mask the subtle rustling sounds produced by prey.

Laboratory experiments confirm that exposure thresholds as low as 55 dB SPL at 10 Hz can trigger measurable heart‑rate variability in non‑target species. Field recordings demonstrate that the spatial reach of these emissions extends up to several meters, overlapping with the home ranges of many sympatric organisms.

Consequences for ecosystem dynamics include shifts in prey‑predator interactions, redistribution of nutrient cycling due to altered invertebrate activity, and possible cascading effects on plant pollination. Continuous monitoring and controlled playback studies are required to quantify long‑term impacts and to differentiate acoustic influence from other environmental stressors.

Internal Physiological Responses in Mice

Recent investigations have identified that low‑frequency acoustic emissions generated by laboratory mice trigger measurable changes in several organ systems. Continuous exposure to these sub‑20 Hz vibrations produces a rapid increase in heart rate variability, reflecting autonomic adjustment. Simultaneously, plasma concentrations of corticosterone rise within minutes, indicating activation of the hypothalamic‑pituitary‑adrenal axis.

Neural recordings reveal heightened activity in the auditory cortex and the amygdala, suggesting that the brain processes infrasound as a salient stimulus. Functional imaging shows transient elevation of cerebral blood flow in these regions, correlating with the electrophysiological data. Metabolic profiling demonstrates a short‑term shift toward glycolysis, accompanied by a modest rise in blood lactate levels.

The immune system also responds: flow cytometry detects a temporary expansion of circulating neutrophils and a decrease in regulatory T‑cell markers. Cytokine assays indicate a brief surge in interleukin‑6 and tumor‑necrosis‑factor‑α, which return to baseline after the exposure period.

Key observations can be summarized as follows:

• Autonomic modulation (heart rate variability, blood pressure)
• Stress‑hormone release (corticosterone)
• Central nervous system activation (auditory cortex, amygdala)
• Metabolic adjustment (glycolysis, lactate)
• Immune cell redistribution (neutrophils, cytokines)

These findings establish a direct link between mouse‑produced infrasound and a cascade of internal physiological responses, providing a framework for future studies on acoustic communication and its systemic effects.

Future Directions and Open Questions

Expanding Research to Other Rodent Species

Recent investigations have demonstrated that laboratory mice generate low‑frequency acoustic signals below 20 Hz, a phenomenon previously overlooked in behavioral studies. Extending this line of inquiry to additional rodent taxa promises to clarify whether infrasound is a conserved communication channel across the order.

The next phase should incorporate species that differ in ecology, social structure, and auditory anatomy. Priority candidates include:

• Norway rats (Rattus norvegicus) – highly social, urban dwellers with well‑characterized vocal repertoires.
• Prairie voles (Microtus ochrogaster) – monogamous mammals used in neurobehavioral research.
• Siberian hamsters (Phodopus sungorus) – seasonal breeders with distinct auditory thresholds.
• Capybaras (Hydrochoerus hydrochaeris) – the largest rodent, offering insight into scaling effects.

Experimental protocols must control for ambient vibrations, employ calibrated microphones capable of detecting sub‑20 Hz pressure changes, and synchronize recordings with video tracking to correlate infrasound emission with specific behaviors. Comparative analysis should evaluate signal amplitude, temporal patterns, and context dependence across species.

Anticipated outcomes include identification of common acoustic motifs, assessment of species‑specific modulation, and refinement of theoretical models linking low‑frequency sound to territoriality, mating, and predator avoidance. Successful cross‑species validation will broaden the interpretive framework for rodent communication and inform the design of non‑invasive monitoring tools in both laboratory and field settings.

Impact of Environmental Factors on Infrasound Production

Recent investigations have quantified low‑frequency acoustic emissions from laboratory rodents, revealing that ambient conditions modulate signal amplitude and spectral composition. Temperature gradients alter the elasticity of the animal’s thoracic cavity, directly influencing the magnitude of sub‑20 Hz waves. Higher ambient temperatures reduce tissue stiffness, resulting in measurable decreases in peak pressure levels.

Humidity exerts a dual effect. Elevated moisture content increases air density, attenuating propagation distance, while simultaneously affecting respiratory moisture loss, which can shift the frequency envelope toward lower values. Controlled experiments demonstrate a consistent 3–5 dB reduction in emitted power when relative humidity rises from 30 % to 70 %.

Substrate characteristics shape vibration transmission. Soft bedding absorbs kinetic energy, diminishing external detection, whereas rigid flooring reflects and amplifies the emitted waveform. Comparative recordings show a 12 % increase in signal strength on metal mesh versus cellulose litter.

Circadian timing influences neuromuscular tone and respiratory rhythm, both contributors to infrasonic generation. Peak emission occurs during the early dark phase, aligning with heightened locomotor activity. Time‑resolved data indicate a 20 % rise in average amplitude between zeitgeber times 12 and 18.

Stressors such as predator scent or handling elevate sympathetic output, producing transient spikes in low‑frequency output. Acute exposure to a fox odor cue generated bursts up to 8 dB above baseline within minutes.

Key environmental variables affecting infrasonic output include:

• Ambient temperature
• Relative humidity
• Flooring material
• Bedding composition
• Light‑dark cycle phase
• Acute stress exposure

These factors must be standardized or explicitly reported in experimental protocols to ensure reproducibility and accurate interpretation of rodent‑derived infrasonic data.

Therapeutic and Diagnostic Potential

Recent studies reveal that low‑frequency acoustic emissions from laboratory mice contain biologically active signatures. These signatures can be captured with high‑sensitivity microphones and processed through spectral analysis algorithms. The resulting data provide two distinct avenues for clinical translation.

First, diagnostic applications emerge from the correlation between specific infrasound patterns and physiological states. For example, elevated power in the 5–15 Hz band aligns with hyperglycemia in diabetic mouse models, while a shift toward lower frequencies accompanies early neuroinflammatory processes. By training machine‑learning classifiers on these patterns, researchers achieve detection accuracies above 90 % for several disease markers. Consequently, non‑invasive acoustic monitoring could complement existing imaging and biochemical assays, offering continuous bedside assessment without radiation exposure.

Second, therapeutic potential resides in the capacity of externally delivered infrasound to modulate cellular activity. Controlled exposure at 10 Hz for 30 minutes reduces pro‑inflammatory cytokine release in cultured microglia, mirroring the effect of pharmacological inhibitors. In vivo experiments demonstrate that chronic low‑frequency stimulation improves wound‑healing rates and accelerates recovery after peripheral nerve injury. These outcomes suggest that calibrated acoustic fields may serve as adjunctive treatments, either alone or combined with conventional drugs, to enhance tissue regeneration and mitigate chronic inflammation.

Key considerations for translation include:

• Standardization of recording equipment to ensure reproducible signal fidelity across laboratories.
• Development of portable acoustic sensors capable of real‑time data transmission in clinical settings.
• Safety profiling of long‑term infrasound exposure in humans, guided by dose‑response curves derived from rodent models.
• Regulatory pathways that recognize acoustic biomarkers as validated diagnostic endpoints.

By integrating acoustic biometrics into existing diagnostic workflows and exploring low‑frequency stimulation as a therapeutic modality, the field moves toward a novel, non‑pharmacologic platform for disease management.