Rats are highly intelligent and social animals that are capable of expressing a wide range of emotions. While rats can’t laugh in the same way humans do, recent research suggests rats do possess a primitive form of laughter that allows them to vocalize positive emotional states.
Evidence that Rats Can Laugh
Studies have found that when rats are playing or being tickled by humans they emit high frequency chirps that appear to indicate happiness or joy. These chirps have been described as laughter by some researchers because they seem to represent a positive emotional response. Here is some of the evidence that rats have the capacity for laughter:
- Rats chirp at frequencies between 50-70 kHz during playful interactions or when tickled.
- These chirps occur when rats are exhibiting behaviors associated with happiness like jumping and running.
- Rats chirp more frequently during positive activities and less in negative situations.
- When rats played and chirped together their chirping synchronized, indicating mutual positive emotion.
- Rats produce chirps in response to hands-on play with humans across different ages, indicating enjoyment.
Based on these findings, scientists believe rats chirp as a way to express happiness, share joy with others, and strengthen social bonds.
How Rat Laughter Developed
Laughter in rats likely evolved as a way for them to communicate positive emotions and intent to others. Here are some of the evolutionary drivers that may have led to rat laughter:
- Being able to signal happiness and form social bonds improved survival and reproductive success.
- Laughing together helped coordinate play between juveniles and cement social affiliation.
- Vocalizing joy when playing reinforced the behavior and improved skills.
- Laughing signals positive intent, defusing potential conflicts.
- Detecting happiness in others provides information about safety/resources in the environment.
The ability to produce laughter-like chirps probably conferred a selective advantage for rats by promoting social cohesion and cooperation. This furthered the survival of individuals, families, and communities of rats.
Neural Basis of Rat Laughter
Researchers have started to explore the neural underpinnings of rat laughter by studying brain changes during chirping:
- Playback of rat laughter chirps causes increased dopamine release, a neurotransmitter linked to pleasure and reward.
- Laughing rats show greater neural activity in limbic areas related to positive emotion like the nucleus accumbens.
- Blocking activity in the medial prefrontal cortex reduces laughing/chirping responses to playful tickling.
- Laughing appears to involve coordinated signaling between the somatosensory cortex, amydala, and periaqueductal gray region.
This indicates laughter in rats arises from activity across multiple emotion, reward, and vocalization centers in the brain. The neural circuitry underlying rat laughter likely shares common evolutionary origins with human laughter.
Comparison to Human Laughter
While rat laughter shares some similarities with human laughter, there are also important differences:
| Human Laughter | Rat Laughter |
|---|---|
| Produced by strong exhalations across vocal folds | Generated by air passing through narrow laryngeal slit |
| Heard as “ha-ha” sounds in 15kHz range | High frequency chirps from 50-70kHz |
| Facial expressions accompany laughter | No distinct facial expressions |
| Intentional social communication | Involuntary expression of positive emotion |
| More cognitive/cortical involvement | More subcortical/brainstem involvement |
While rat laughter may be considered more primitive and less volitional than human laughter, both appear to serve similar social bonding functions.
Conclusion
Rats are capable of expressing laughter-like vocalizations when they play, are tickled, or experience other happiness. This suggests rats have a basic form of social laughter that evolved to promote social affiliation. While rats can’t laugh exactly like humans, their capacity for primitive laughter provides insight into the neural basis of positive emotions and social bonding across mammals. Rat laughter shows that a common ancestor likely possessed primordial neural circuitry to produce laughter-like sounds during positive states. This then evolved into more complex forms of mammalian laughter like that seen in humans. So the basic neurological capacity for laughter appears widespread in mammals even if it sounds different across species.