Oxytocin May Help the Brain Recognise When Danger Has Passed

Oxytocin is widely associated with love, trust and bonding. Yet scientists have found evidence that brain cells responsive to the so-called "love hormone" could also help us identify when a threat is over.

Its status as a simple social chemical has been challenged for some time. Oxytocin's effects may vary with the circumstances, an individual's emotional state, and whether another individual is regarded as safe or dangerous.

Experiments in mice have identified a small population of neurons expressing oxytocin receptors that seems to affect both social approach and fear extinction - the learning process through which something once linked with danger is recognised as safe.

Published in Brain, the research identifies the paraventricular thalamus (PVT) as a potential point where social behaviour and fear intersect. The results may offer an early indication of why both functions can be impaired in conditions including autism and anxiety disorders.

Oxytocin-sensitive neurons in the paraventricular thalamus

To investigate oxytocin's differing effects, researchers in Japan examined oxytocin-sensitive neurons within the PVT, a brain area involved in stress, motivation and emotional behaviour.

The scientists used genetically modified male mice and selectively inhibited or stimulated the neurons, assessing the consequences for social behaviour and fear extinction.

Inhibiting these neurons made the mice less interested in engaging with unfamiliar animals. This lower level of social interaction appeared in two separate social-behaviour tests, and could not be explained by reduced movement or increased anxiety.

(Evgenyi_Eg/Getty Images)

Stimulating the same neurons, however, did not make the mice more sociable. The findings imply that while the cells may be required for typical social behaviour, activating them alone is insufficient to raise social interest.

How the cells affect fear extinction

The team next investigated fear extinction.

Initially, mice were taught to link a particular environment with a mild electric shock. They were then placed back in that environment repeatedly without experiencing any further shocks.

Inhibiting the oxytocin-sensitive neurons did not stop the animals establishing the initial fear memory. But when they re-entered the environment, which was now safe, the mice still froze - staying motionless as an indication of fear. This indicated that they struggled to learn that the threat was gone.

Stimulating the neurons had another effect. During the initial phase of fear-extinction learning, the mice froze less, although the effect was no longer evident when they were tested the next day or one week afterwards.

Conversely, manipulating comparable oxytocin-sensitive neurons in other parts of the brain did not change the animals' sociability. This indicates that the contribution of such cells to social behaviour depends on their location.

This regional distinction is significant, since oxytocin does not trigger an identical social response in every neural circuit. A 2024 review published in Hormones and Behavior, which drew on studies of California mice, likewise concluded that oxytocin may encourage either social approach or social avoidance according to the context and brain circuits involved.

(PixelsEffect/Canva)

Early evidence in humans and limitations

The researchers also searched for signs of a relationship between oxytocin, the thalamus and social traits in people.

They examined information from 30 Japanese adolescents: 19 with a diagnosis of autism spectrum disorder and 11 typically developing participants. The team compared salivary oxytocin concentrations with MRI measurements of the thalamus and evaluations of autism-related traits.

They identified associations among oxytocin levels, thalamic characteristics and certain behavioural measures. However, the analysis was small and exploratory, while oxytocin in saliva may not represent the hormone's activity in the brain.

The animal work has notable constraints too. Most of the research involved male mice, and artificial activation of the targeted group of neurons with oxytocin receptors does not replicate the brain's natural release of the hormone.

Consequently, these findings do not yet establish that naturally released oxytocin directly governs social behaviour or fear extinction.

Related: Scientists Identify a Brain Mechanism That Regulates Fear in Mice

Should subsequent research verify a comparable system in humans, it may help scientists understand conditions marked by challenges with social behaviour or fear regulation, including autism and anxiety disorders, more clearly.

For the moment, the results indicate that oxytocin's influence relies on exactly where and when it acts in the brain - potentially affecting both social approach and the capacity to recognise that danger has passed.

The study was published in Brain.

This article was fact-checked by Michael Irving and edited by Michael Irving. Although we take pride in our process, we are only human. If you notice an error, please let us know.