Rats have a surprisingly rich vocal repertoire that splits into two broad systems: ultrasonic calls pitched far above human hearing, and audible sounds we can actually detect. The ultrasonic calls are the workhorses of rat communication, falling into a low-frequency group around 22 kHz that signals distress or danger and a high-frequency group in the 40–80 kHz range tied to positive experiences like play and mating. These aren’t random noises. Each type of call carries specific emotional information and triggers predictable reactions in other rats, making rat vocalization one of the more useful windows researchers have into animal emotion.
The Two Big Categories of Ultrasonic Calls
Most of what rats “say” to each other happens in a frequency range humans can’t hear at all. Rat ultrasonic vocalizations, or USVs, cluster into two families that map roughly onto negative and positive emotional states. The low-frequency family centers around 22 kHz and shows up during fear, pain, social defeat, and other aversive situations. The high-frequency family sits in the 40–80 kHz range and appears during play, mating, anticipation of food, and other rewarding contexts.1PubMed Central. Rat 50 kHz Trill Calls Are Tied to the Expectation of Social Interaction The split isn’t absolute, and context matters, but as a rule of thumb: low pitch means something bad, high pitch means something good.
What makes this system interesting is that it isn’t just a reflex. Rats adjust their calling behavior depending on who’s around, what’s happening, and what they’ve learned from past experience. The acoustic properties of the calls, their duration, frequency contour, and how often they’re repeated, change with the situation. And critically, the calls change other rats’ behavior in ways that match the emotional content, functioning as genuine social signals rather than involuntary outbursts.2Physiology & Behavior. The effect of playback of 22-kHz and 50-kHz ultrasonic vocalizations on rat behaviors assessed with a modified open-field test
22 kHz Calls and the Language of Fear
The 22 kHz call is the one researchers understand best. It’s a long, relatively monotone ultrasonic sound that rats produce when they’re frightened, in pain, or facing a threat. These calls serve as alarm signals. When one rat starts emitting 22 kHz vocalizations, nearby rats respond with avoidance, freezing, and other anxiety-related behaviors. Brain imaging during playback of these calls shows activation in regions associated with negative emotion, including the amygdala, which processes threat, and the periaqueductal gray, which coordinates defensive behavior.3PubMed Central. Playback of rat 22-kHz ultrasonic vocalizations as a translational assay of negative affective states
The alarm-call function has been tested directly. In one experiment, researchers showed that when a rat that had received a foot shock was placed near a naive rat, the naive rat picked up on the fear and began freezing too. The key transmission channel turned out to be the 22 kHz calls. Rats whose auditory relay nuclei had been surgically disabled showed no fear response to a terrified cagemate, even though that cagemate was freezing and presumably emitting fear-related odors. Without the ability to process the ultrasonic calls, the emotional contagion didn’t happen.4PLOS ONE. Social Transmission of Fear in Rats: The Role of 22-kHz Ultrasonic Distress Vocalization This tells us something important: while smell and visual cues play supporting roles, the ultrasonic alarm call is the primary vehicle for spreading fear through a group.
The neural circuit behind 22 kHz calls involves the dorsal periaqueductal gray, a brainstem structure that sits at the crossroads of pain processing and defensive behavior. Electrical stimulation of this region in rats produces the full package of fear responses, including bursts of activity, freezing, and 22 kHz vocalizations, all wired together as a coordinated defense program.5PubMed Central. Dorsal periaqueductal gray-amygdala pathway conveys both innate and learned fear responses in rats
50 kHz Calls and the Sound of Good Times
The high-frequency family of calls is more varied and, frankly, more fun. Rats emit a range of brief sounds in the 30–80 kHz range during positive experiences: rough-and-tumble play with cagemates, mating encounters, anticipation of a treat, or even when they’re about to see a familiar companion. Unlike the relatively uniform 22 kHz alarm call, the 50 kHz family includes multiple subtypes. Some are “flat” calls with a steady pitch. Others are “trills” with a rapid frequency modulation around 100 Hz. Still others show sudden frequency jumps. These elements can combine within a single call, producing what one research group described as a potentially large “dictionary” of signals.6Frontiers in Behavioral Neuroscience. Rats Synchronize Locomotion with Ultrasonic Vocalizations at the Subsecond Time Scale
Among these subtypes, the frequency-modulated trill appears to be especially tied to social anticipation. Research has found that trill calls spike when rats expect a social interaction is about to happen, suggesting they may serve a contact-seeking or bonding function beyond just reflecting a general good mood.1PubMed Central. Rat 50 kHz Trill Calls Are Tied to the Expectation of Social Interaction Whether each subtype in the 50 kHz family carries a distinct message or whether they all represent variations on a single “positive” theme is still an open question, but the evidence is trending toward some degree of specificity.
The brain circuitry behind 50 kHz calls overlaps heavily with the reward system. Studies using electrode mapping, targeted brain lesions, and pharmacological manipulation have shown that the neural circuit driving these calls closely matches the circuit for drug reward, self-stimulation reward, and the mesolimbic dopamine pathway.7Behavioural Brain Research. Neurobiology of 50-kHz ultrasonic vocalizations in rats: Electrode mapping, lesion, and pharmacology studies In plain terms, 50 kHz calls come from the same part of the brain that makes rats seek out things they enjoy. The calls aren’t just correlated with positive states; they’re wired into the pleasure circuitry itself.
What Happens When Other Rats Hear These Calls
Rat calls aren’t just emotional expressions floating into the void. They change the behavior of listeners in predictable, emotion-appropriate ways. When male rats hear playback of 22 kHz alarm calls, they show a pattern of defensive responses: reduced exploration, increased vigilance, and avoidance of open areas. When the same rats hear playback of frequency-modulated 50 kHz calls, the pattern reverses. They explore more, move more freely, and approach the source of the sound.2Physiology & Behavior. The effect of playback of 22-kHz and 50-kHz ultrasonic vocalizations on rat behaviors assessed with a modified open-field test The emotional content of the calls appears to transfer to the listener, a form of emotional contagion that may function as the rat equivalent of empathy, or at least of shared vigilance and shared enthusiasm.
This listener effect has real welfare implications. In a colony of lab rats, if one animal is experiencing chronic stress and emitting 22 kHz calls, those calls can raise anxiety levels in every other rat within earshot. The stress isn’t contained to the individual; it radiates through the group via the acoustic channel. Research has confirmed that 22 kHz calls can induce a negative emotional state of increased anxiety in non-calling cagemates, making the vocalizations a useful welfare indicator not just for the caller but for the entire group.8Applied Animal Behaviour Science. Ultrasonic vocalizations as indicators of welfare for laboratory rats (Rattus norvegicus)
Audible Sounds You Can Actually Hear
Not everything rats say is ultrasonic. When rats experience sudden, sharp pain, they produce audible squeaks that fall within the range of human hearing. These squeaks serve a different social function from the sustained ultrasonic calls. While 22 kHz calls are sustained alarm signals emitted during prolonged fear or distress, pain squeaks are brief, reactive sounds tied to acute noxious events. Research has shown that audible pain squeaks can trigger emotional contagion in nearby rats, particularly those that have had prior exposure to similar painful experiences, suggesting a form of learned empathic response.9PubMed Central. Audible pain squeaks can mediate emotional contagion across pre-exposed rats with a potential effect of auto-conditioning
Wild rats also produce audible defensive-threat vocalizations, sometimes called sonic calls, when a predator gets very close. These differ from ultrasonic alarm calls in their context. Whereas 22 kHz calls tend to accompany freezing and avoidance in response to a distant threat, sonic defensive calls appear when a threat is proximate and escape isn’t possible. The rat essentially switches from “warn the group and hide” to “sound aggressive and try to deter the predator.”
Baby Rats and the Calls That Bring Mom Running
Rat pups begin vocalizing almost immediately after birth, but their calls are distinct from the adult repertoire. When separated from their mother and littermates, pups as young as a few days old emit ultrasonic distress calls in the 30–50 kHz range.10PubMed. Models of anxiety: ultrasonic vocalizations of isolated rat pups The rate of calling goes up with the severity of the stressor. A pup placed on a cold surface calls more than one placed on a warm surface, and both call more than a pup that remains with its family.
These isolation calls serve a clear biological purpose: they prompt the mother to retrieve the pup. The acoustic properties of pup calls also appear to interact with other sensory cues. Research has found that the combination of ultrasonic calls and specific anogenital odors from the pup works together to trigger maternal licking behavior, with the calls acting as the initiating signal and the odor guiding the specific caregiving response.11Behavioural Brain Research. Role of pups’ ultrasonic calls in a particular maternal behavior in Wistar rat: pups’ anogenital licking
As pups mature, the acoustic characteristics of their calls shift. The heightened call rate during isolation reflects anxiety, while other features like frequency and duration track developmental stage rather than emotional state. Call duration in control pups tends to decrease as they age, with shorter calls appearing by the twelfth day after birth compared to the sixth day.12Scientific Reports. Infant rat ultrasonic vocalizations in the neurodevelopmental model of schizophrenia By the time pups are weaned, their vocalizations have matured into the adult pattern of 22 kHz and 50 kHz calls.13PubMed. Development of ultrasonic calls in rat pups follows similar patterns regardless of isolation distress
Sex Differences in Rat Vocalizations
Male and female rats don’t vocalize identically. In pups, the pattern shifts with age. Very early in development (before about postnatal day eight), female pups emit longer calls than males. After that point, the pattern reverses and males produce longer calls.14PubMed Central. A meta-analysis of sex differences in neonatal rodent ultrasonic vocalizations and the implication for the preclinical maternal immune activation model This reversal matters for researchers using pup vocalizations as a measure of anxiety or neurodevelopment, since ignoring sex as a variable can lead to conflicting results across studies.
In adults, sex differences persist. Playback studies have found that 50 kHz calls from females increase appetitive exploratory behavior in male listeners, while 22 kHz calls from males produce defensive responses.2Physiology & Behavior. The effect of playback of 22-kHz and 50-kHz ultrasonic vocalizations on rat behaviors assessed with a modified open-field test The sex of the caller may add a layer of meaning to the call’s emotional content, though untangling this from basic acoustic differences between male and female voices is an ongoing challenge.
Tickling Rats and “Laughter”
One of the more striking findings in rat vocalization research came from Jaak Panksepp’s lab, which discovered that rats produce a distinctive pattern of 50 kHz chirps when tickled by a human hand. Panksepp proposed that these chirps may be a primitive form of laughter, evolutionarily related to the joyful vocalizations human children make during social play.15PubMed. “Laughing” rats and the evolutionary antecedents of human joy? The idea generated considerable interest and some skepticism. Rats that are tickled do seek out more tickling, approach the tickling hand, and show other signs of enjoying the experience. No aversive 22 kHz calls appear during tickling, confirming it’s a positive experience for the animal.16Philosophical Transactions of the Royal Society B. Who’s laughing? Play, tickling and ultrasonic vocalizations in rats
Whether “laughter” is the right word remains debated. The 50 kHz calls during tickling are similar to those during rat-to-rat play, but some researchers have questioned whether human tickling truly simulates what happens between two playing rats, or whether it just activates the same reward circuitry through a different route. Either way, the practical takeaway is real: brief tickling sessions can improve welfare in lab rats and have been adopted by some facilities as a form of enrichment.
How Rats Physically Produce Ultrasonic Calls
Ultrasonic calls are not produced the way most mammalian vocalizations are. Humans and most other mammals make sound by vibrating their vocal folds, but rats generate ultrasonic frequencies through a fundamentally different mechanism. Research using laryngeal reconstruction and airflow measurements has shown that rats produce USVs by directing a jet of air from the glottis at a structure inside the larynx. One line of evidence points to an “edge-tone” mechanism, where the glottal jet hits the alar edge and creates oscillations amplified by a small chamber called the ventral pouch, which may function like a resonator. When researchers made small lesions to this ventral pouch, ultrasonic call production changed dramatically.17PubMed Central. Laryngeal airway reconstruction indicates that rodent ultrasonic vocalizations are produced by an edge-tone mechanism
More recent work has refined this picture, showing that USVs are produced by a “wall impingement whistle” mechanism, in which the glottal jet hits the inner wall of the thyroid cartilage.18PubMed Central. Aerodynamics and motor control of ultrasonic vocalizations for social communication in mice and rats The details are still being sorted out, and the two models may describe slightly different aspects of the same process. What’s clear is that ultrasonic calling doesn’t require vocal fold vibration, which is why rats can produce these sounds at such high frequencies. The calls are tightly coordinated with breathing. Each call is essentially a shaped exhalation, and the rhythm of calling tracks closely with the respiratory cycle throughout the rat’s life.19Europe PMC. Ultrasonic Vocalizations Emission across Development in Rats: Coordination with Respiration and Impact on Brain Neural Dynamics
Rat Calls as Tools in Biomedical Research
Because rat vocalizations map so reliably onto emotional states, they’ve become valuable tools for studying brain disorders and testing potential treatments. Vocalizations provide a behavioral readout that complements traditional measures like locomotion and freezing. When a rat in a depression model produces fewer 50 kHz calls, or a rat in an anxiety model ramps up 22 kHz calls, those changes track the emotional disruption in a way that movement-based tests alone may miss. Researchers have argued that integrating vocalization analysis into studies of brain injury and neurological disease could improve how we evaluate treatments targeting mood and anxiety.20Behavioural Brain Research. Ultrasonic Vocalizations as Markers of Anxiety and Depression in Rodent Models of Neurotrauma
Vocalizations have also proven useful in memory research. After fear conditioning, rats emit frequency-modulated USVs that can serve as a sensitive marker of how strongly they’ve encoded an aversive memory. This has practical relevance for testing drugs aimed at weakening traumatic memories, a line of research with obvious implications for PTSD treatment. Including vocalization measures in these experiments gives researchers a more nuanced picture of whether a treatment is truly reducing the emotional impact of a memory or just suppressing the motor response of freezing.21PubMed Central. Rat Ultrasonic Vocalizations as an Index of Memory
More broadly, rat and mouse USVs are applied across a wide range of biomedical fields, from neurodevelopmental models to pharmacological screening, because they provide information about the animal’s emotional and health status that other behavioral tests don’t capture as well.22PubMed. Mouse and rat ultrasonic vocalizations in neuroscience and neuropharmacology: State of the art and future applications
Monitoring Welfare Through Sound
The link between vocalizations and emotional states has a straightforward practical application: you can eavesdrop on a colony of rats to assess how they’re doing. If researchers or animal care staff record ultrasonic vocalizations from home cages, the ratio of 22 kHz to 50 kHz calls gives a real-time readout of group wellbeing. One study examining the effects of cage enrichment used a 14-call-type classification scheme and found that housing conditions significantly affected vocalization patterns, though the results were more complex than expected. Rats in enriched cages actually produced fewer 50 kHz calls and had higher stress hormone levels, possibly because enrichment items created competition and more social friction.23PubMed Central. Ultrasonic Vocalization Analysis as a Novel Metric to Assess Cage Enrichment in Rats The finding highlights that “enrichment” doesn’t always work the way we assume, and that vocalization monitoring can catch subtleties that cage-side observation misses.
The approach scales beyond individual studies. Since 22 kHz calls can raise anxiety in nearby rats who are simply within earshot, a single distressed animal can degrade the welfare of an entire room of animals. Monitoring for 22 kHz calls across a facility could, in principle, flag welfare problems before they become visible through weight loss, reduced food intake, or other traditional indicators.8Applied Animal Behaviour Science. Ultrasonic vocalizations as indicators of welfare for laboratory rats (Rattus norvegicus)
How Researchers Actually Detect These Calls
Since humans can’t hear ultrasonic vocalizations, studying them requires specialized equipment: microphones sensitive to frequencies above 20 kHz and software that can identify, classify, and count calls in large audio datasets. Until recently, call detection and classification were done manually by researchers scrolling through spectrograms, a process that was accurate but painfully slow. A tool called DeepSqueak, developed using deep-learning neural network architecture, automated this process. It detects and classifies USVs with accuracy comparable to human analysts but at vastly greater speed.24PubMed Central. DeepSqueak: a deep learning-based system for detection and analysis of ultrasonic vocalizations The system has since been adapted for use with other species as well, though its performance varies depending on call type and detector configuration.25Scientific Reports. Utilizing DeepSqueak for automatic detection and classification of mammalian vocalizations: a case study on primate vocalizations
The availability of automated detection tools has opened up research questions that were previously impractical to address. Instead of sampling short recording windows, researchers can now analyze continuous recordings over hours or days, capturing the full temporal dynamics of how calling behavior changes with circadian rhythms, social interactions, and experimental manipulations. For pet rat owners curious about what their animals are “saying,” consumer-grade bat detectors can pick up some ultrasonic vocalizations and shift them into the audible range, though the resolution is far coarser than what lab equipment provides. Still, hearing even a rough version of your rat’s 50 kHz chirps during playtime is a surprisingly compelling experience.