This is a repost from the old WordPress incarnation of Not Exactly Rocket Science
You are being hunted, chased through a labyrinth by a relentless predator. Do you consider your options and plan the best possible escape, or do you switch off and rely solely on instinct? A new study provides the answer – you do both, flicking from one to the other depending on how far away the threat is.
Earlier studies have found that different parts of a rodent’s brain are activated in the face of danger, depending on how imminent that danger is. Now, scientists at University College London has found the same thing in human brains.
It would be a poor strategy to stick to the same defensive behaviours in all situations. Simply put, there are threats and there are threats, and we need different kinds of behaviour to cope with different scales of danger. When a predator is fifty feet away, we have the time and space to consider our options and plan an escape. But when it’s five feet away, such luxuries are ill-afforded and behaviour needs to be fast and reflexive. In the millisecond between life and death, the best laid plans of mice and men take a back seat in the light of three simple options – fight, flight or freeze.
This sounds fairly obvious, but Dean Mobbs and colleagues actually watched the switch taking place by scanning the brains of several volunteers as they were being chased by a predator. Of course, ethics committees would frown on letting a bear loose on some volunteers, so the experiment was done in a virtual Pacman-like game, where people had to flee a virtual predator through a maze. But they weren’t completely let off the hook; if they were caught, they received an electric shock.
If you wanted to turn a rat into a fearless critter, unfazed by cats or bigger rats, the best way would be to neutralise a small pair of tiny structures in its brain called the dorsal premammillary nuclei, orPMD. According to new research by Simone Motta at the University of Sao Paolo, these small regions, nestled within a rat’s hypothalamus, control its defensive instincts to both predators and other rats.
But not all neurons in the PMD are equal. It turns out that the structures are partitioned so that different bits respond to different threats. The front and side parts (the ventrolateral area) are concerned with threats from dominant and aggressive members of the same species. On the other hand, the rear and middle parts (the dorsomedial area) process the threats of cats and other predators. And both areas are distinct from other networks that deal with the fear of painful experiences, such as electric shocks.
This complexity is surprising. Until now, scientists have mostly studied the brain’s fear system by focusing on an area called the amydgala, which plays a role in processing memories of emotional reactions. And they have generally assumed that fearful responses are driven by the same networks of neurons, regardless of the threat’s nature.
There’s good reason to think that. Hesitating in the face of danger is a sure-fire way to lose one’s life, so animals respond in a limited number of instinctive ways when danger threatens. They freeze to avoid detection, flee to outrun the threat, or fight to confront it. These automatic “freeze, fight or flight” responses are used regardless of the nature of the threat. Rats, for example, behave in much the same way when they are menaced by cats or electrified floors alike, and actually find it very difficult to do anything else.
This limited repertoire of action convinced scientists that animals process different fears in the same way, relying on the same network of neurons to save their hides from any and all threats. Motta’s research shows that this idea is wrong, certainly for rats and probably for other mammals too. The brain’s fear system isn’t a one-size-fits-all toolkit; it has different compartments that respond specifically to different classes of threats.