Tickled rats reveal how human-animal bonds form in the brain

Touch is the oldest language of bonding. From a parent cradling an infant to grooming among primates, pleasant tactile stimulation sparks attachment across the animal kingdom.

A new study pushes that insight a step further, showing that the same principle can cross species lines: young rats repeatedly “tickled” by human fingers start to seek out those hands, and their brains rewire to make the contact feel rewarding.

Rats laugh during rough play

Juvenile rats love rough‑and‑tumble play. When they tussle, they emit rapid bursts of ultrasonic calls around 50 kHz – inaudible to us but easy to pick up with microphones. Neuroscientists interpret these chirps as a sign of joy.

Earlier work showed that rats produce the same 50 kHz giggles when a person lightly strokes and flips them, imitating play wrestling. With enough sessions, the animals begin to follow the experimenter’s hand, eager for more.

In the new research, a team led by Dr. Himeka Hayashi and Professor Hirotaka Sakamoto from Okayama University tickled adolescent rats for five minutes twice a day over ten days.

At first, the animals chirped only occasionally, but starting on day five, they consistently produced such vocalizations in response to tickling. By day ten the calls poured out, clear evidence that repeated touch felt good.

Preference grows for human touch

After the training, the scientists ran a conditioned place preference test. Each rat could roam between two chambers, one linked to tickling in earlier sessions and one neutral.

The animals spent a larger amount of time in the tickling room after the test as compared to before, a behavioral sign that they now preferred the place associated with human hands.

The finding delighted the researchers on a personal level. “We have always been curious about how humans and animals can form bonds despite having no shared language or lifestyle,” Hayashi said.

“We wondered whether the connection we felt with animals was real or just our imagination. Through this study, we discovered that rats genuinely enjoy interacting with us – which brought us great happiness.”

Touch and human-animal bonding

Pleasure alone was only half the story. The researchers also wanted to see what changed inside the brain. They focused on the ventrolateral part of the ventromedial hypothalamus, or VMHvl, a region already linked to social behaviors in rodents.

After the ten‑day regimen the rats showed increased expression of oxytocin receptors in that hub. Oxytocin, often called the bonding hormone, surges during maternal care, pair bonding, and even friendly hugs in humans.

To test cause and effect, the scientists blocked oxytocin signaling specifically in the VMHvl. The result was striking. Without that chemical handshake, the rats’ new fondness for human touch faded.

Touch connects hormone to behavior

Where does the oxytocin come from? Using neural tracing techniques, the team followed fibers leading into the VMHvl and identified a subset that starts in the supraoptic nucleus, a part of the brain that houses magnocellular neurons known for pumping out oxytocin.

Those long projections suggest a direct anatomical route by which tactile joy travels from a high‑level hormone center to the limbic machinery that tags experiences as good or bad.

“We revealed part of the neural circuitry underlying why naturally wary animals become attached to humans,” Hayashi explained.

“We discovered that during the process of rats becoming tame to human hands, the action of oxytocin in a specific brain region (VMHvl) mediates the effects of pleasant tactile stimulation and controls the formation of social bonds across species.”

Human-animal bonding beyond rats

Most companion‑animal owners sense that stroking a cat or dog soothes both parties. The new results give that intuition a mechanistic footing and hint at therapeutic spin‑offs.

“The discovery that pleasant tactile stimulation facilitates cross‑species social bonding could lead to a better understanding of the neural mechanisms underlying both social interaction difficulties and the therapeutic effects of physical contact with animals such as cats and dogs,” Hayashi said.

“This knowledge may contribute to the development of novel therapeutic and support approaches for individuals who struggle with social interactions.”

Nearly 150 years after Darwin wondered how new social ties emerge, the answer for rats and humans appears remarkably simple: persistent, playful touch tunes the same ancient hormone system that once glued mothers to pups.

Unlocking that circuit not only turns skittish rodents into willing partners but may also open doors to treatments that use controlled touch to ease loneliness and boost social confidence in people.

The study is published in the journal Current Biology.

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