Safety becomes more important than foraging when a specific neuronal circuit in the brain is activated

Now researchers from the Department of Neuroscience and the Center for Basic Metabolic Research at the University of Copenhagen have identified a neural circuit in the mouse’s brain which ensures that it prioritises safety over other needs, e.g. food seeking, and that this happens automatically when this part of the brain is activated.

Neural circuit in the mouse’s brain prioritises safety

Basically, what the researchers have discovered is an evolutionary survival mechanism in the mouse’s brain. It connects part of the hypothalamus (the lateral hypothalamus) to and area of the brainstem – the pedunculopontine nucleus- that plays a key role in initiating movement.

When active, the network sets aside other needs such as food seeking and social contact and makes the mouse run for cover.

In other words, the mouse’s movements are not triggered by external stimuli such as the sight of an owl or a hawk, but by a safety mechanism in the brain that makes sure the mouse automatically and regularly returns to safety.

“By focussing on this particular circuit in the brain between the lateral hypothalamus and the pedunculopontine nucleus, we have been able to describe the neuronal foundation of a very complex innate behaviour. Our results explain how the brain translates abstract assessments of danger into concrete action such as running for cover.

This study thus fills a gap in our understanding of how motivation and movement are connected in the brain,” says Nathalie Krauth, who is first author of the study, “A hypothalamus-brainstem circuit governs the prioritization of safety over essential needs”, which has just been published in Nature Neuroscience.

What did they do? Behavioural experiments and brain cell stimulation

Using a combination of behavioural experiments and optogenetics, the researchers stimulated specific nerve cells in the brains of mice by shining a light on the brain cells they wanted to examine. In the experiment, they first denied the animals access to food, before they allowed them to look for food in a large arena.

When the researchers then stimulated the nerve cells in the lateral hypothalamus that are connected to the pedunculopontine nucleus, the mouse would run away from the food and return to safety. This behaviour repeated itself when a mouse of the opposite sex was present. “It is clear that this specific circuit in the brain prioritises safety-related movement over movements or behaviour related to food seeking or social needs, which are controlled by different circuits in the hypothalamus,” says Christoffer Clemmensen, one of the senior authors of the study.

From mouse brain to human brain

The mouse brain is useful in research because it in many ways resembles the human brain and shares some of the same structures. Professor Ole Kiehn, one of the senior authors of the study, therefore places the new results in a larger context.

“The lateral hypothalamus and the pedunculopontine nucleus, which play a key role in initiating movement – as our research group has previously shown – are found in the brain of all vertebrates, including humans. So even though a lot of species, humans included, are not prey as such, it is likely that similar circuits are vital to the universal balancing of needs fulfilment and avoiding danger.

Because the circuit we have discovered can also be affected by external signals that may serve as learning cues, it is possible that the circuit is affected by stressful situations that may eventually lead to increased anxiety.”

And so, as all basic research, the results of the study pave the way for new questions and investigations.