Mouse Study Reveals Brain Switch Behind Flee Or Freeze Response

Researchers person identified a cardinal neural move that controls whether animals instinctively fly from a threat aliases frost successful place. By comparing 2 intimately related deer-mouse species, they recovered that this move is calibrated by improvement to lucifer nan animal's habitat. This neural circuit is hypersensitive successful mice surviving successful densely vegetated environments, causing instant escape, but little responsive successful their open-field cousins, who are much apt to freeze. In doing so, nan investigation squad uncovered an important measurement successful which improvement fine-tunes nan encephalon for survival.

Flee aliases freeze?

In nature, endurance hinges connected making nan correct split-second prime erstwhile threat strikes, and nan brain's protect circuits are built for precisely that task. Yet what counts arsenic nan "right" consequence depends connected nan landscape: successful cluttered woods, swift formation into nan underbrush tin prevention your life; connected exposed grassland, motionless hiding buys time. How does improvement lick this puzzle? 

In a caller study published successful Nature, an world investigation squad from Belgium and nan USA has uncovered an elegant system that, by tweaking nan sensitivity of a danger-response hub successful nan brain, tailors behaviour to each situation without redesigning nan full system.

Forest mice vs open-field mice

When a protector of a imaginable predator looms overhead, wood mice (Peromyscus maniculatus) dash for cover, while their open-field cousins (Peromyscus polionotus) frost successful place. The researchers group retired to pinpoint nan encephalon move that sets those other instincts.

To precisely measurement flight behavior, we presented some types of mice pinch stimuli that resembled an aerial predator successful a controlled environment. We recovered that open-field mice required astir doubly nan stimulus strength to trigger flight compared pinch their wood relatives, indicating a important quality successful really they processed nan threat stimulus."

Felix Baier, co-first writer and portion of nan investigation squad astatine Harvard

A move successful nan brain

Using cutting-edge neural recordings pinch Neuropixels probes and manipulation techniques, nan researchers traced these behavioral differences to a cardinal bid hub for flight actions: nan dorsal periaqueductal grey (dPAG), a group of neurons heavy successful nan brain. "We were amazed to find that improvement acted successful a cardinal encephalon region, downstream of peripheral sensory perception, because for improvement to alteration a behavior, it has often been thought that nan easiest and astir businesslike measurement would beryllium to conscionable alteration nan sensory inputs," says Baier.

Both type comprehend nan looming threat identically arsenic evidenced by comparable responses on nan circuit from nan oculus to nan dPAG erstwhile nan animals saw nan stimulus without reacting to it. However, nan activation of nan dPAG differed importantly successful nan lawsuit wherever nan mice escaped from nan threat.

"Our monitoring of neural activity revealed a stark contrast: successful wood cervid mice, escaping from a imaginable threat successful nan entity is enabled by an instant 'run' bid successful nan dPAG, whereas nan dPAG of its unfastened section relative does not nonstop immoderate specified commands. This divergence tin beryllium understood arsenic an evolutionary repurposing of neural circuits to finetune endurance response," says Katja Reinhard, who is nan different co-first writer and a erstwhile postdoc astatine NERF (part of imec, KU Leuven and VIB), now starring her ain group astatine SISSA, Italy.

Further, by utilizing precocious methods that fto scientists activate aliases soundlessness circumstantial encephalon regions, nan squad demonstrated a causal connection. Artificially stimulating dPAG neurons successful wood mice made them flight moreover successful nan absence of a threat. Conversely, utilizing chemic methods to dampen dPAG activity raised their flight threshold, making their behaviour much for illustration that of their cousins. 

Built-in flexibility

The study not only sheds ray connected really instinctive behaviors for illustration freezing aliases fleeing are controlled but besides underscores nan elasticity of nan brain's soul architecture, explicate lead authors Prof. Karl Farrow (imec, KU Leuven, VIB) and Prof. Hopi Hoekstra (Harvard).

Farrow: "By comparing these 2 related type we uncovered a move that balances frost versus flight, showing really earthy action fine-tunes behaviour without rewiring nan senses."

Hoekstra: "Our caller find illustrates a basal evolutionary principle: earthy action often tweaks existing neural circuits alternatively than constructing wholly caller pathways."