Tag Archives: Freeze

Danger sign.

Scared? Here’s how your brain decides whether you freeze, flee, or fight

New research sheds light on how our brains react when faced with danger.

Danger sign.

Image credits spcbrass / Flickr.

Hear that? If you listen really hard, you can actually make out the sound of nothing hunting you right now. Safely ensconced in our society, we tend to take this for granted. Make no mistake, however: it’s anything but.

That’s exactly why we (and basically every other animal) evolved from the ground up with self-preservation in mind. Despite our sheltered existence, the brain circuits that generate our responses to perceived threats are still very much alive to this day. In a bid to better understand how these networks operate, and why they work the way they do, researchers at the Champalimaud Centre for the Unknown (CCU) in Lisbon, Portugal, set about to terrify the pants off some very tiny flies.

Fly, fruit fly!

“Just like any other animal in nature, our reaction to a threat is invariably one of the following three: escape, fight or freeze in place with the hope of remaining unnoticed,” says Marta Moita, co-lead author of the study.

“These behaviours are fundamental, but we still don’t know what the rules of the game are,” adds the study’s first author Ricardo Zacarias. “In each situation, how does the brain decide which of the three strategies to implement and how does it ensure that the body carries it through?”

Fruit flies (Drosophila melanogaster) might not seem like the coolest or smartest organism out there — in all honesty, they’re not — but they do have a few saving graces: they’re easy and cheap to care for in large numbers and they’re low maintenance. They also procreate fast and with a fury, so there’s always plenty of them to experiment on.

Given their simpler natures (and wings), Moita admits, many people “believed that flies only escape”, but the research showed that’s not the case. They devised an experiment in which the flies didn’t have the option of flying away and then spooked them to see their reaction.

The flies were placed in covered dishes and were then shown an expanding dark circle, which ” is how a threat looks like to a fly,” Moita explains. With flying away out of the question, the flies froze, the team reports. In a perfect mirror of the same behavior in mammals, birds, and several other species, the flies remained completely motionless for minutes on end. There’s no doubt as to why the flies froze since they would maintain positions that were obviously awkward and uncomfortable for them, such as half crouches, or holding a leg or two “suspended in the air,” Moita explains.

Some flies, however, decided to make a dash for it.

“This was very exciting,” says Vasconcelos, “because it meant that similarly to humans, the flies were choosing between alternative strategies.”

The next step was to take a closer look at what triggered each response. For this goal, the team used machine vision software to produce highly-detailed accounts of each fly’s behavior. Analyzing this data revealed that the flies’ response was determined by their walking speed at the moment the threat appeared. If the fly was walking slowly, it would freeze. By contrast, if it was traveling at speed, it would attempt to run away instead.

“This result is very important: it is the first report showing how the behavioural state of the animal can influence its choice of defensive strategy,” Vasconcelos points out.

The team later identified a single pair of neurons that underpin these defensive behaviors. The pair — with one neuron on each side of the flies’ brain — decided whether the flies would freeze or not. When the team inactivated these neurons, the flies stopped attempting to freeze and just ran away from threats all the time.

When the team artificially forced the neurons to stay active all the time, even without a threat being present, the flies would freeze depending on their walking speed — the fly would freeze if it was walking slowly, but not if it was walking quickly.

“This result places these neurons directly at the gateway of the circuit of choice,” says Zacarias.

“This is exactly what we were looking for: how the brain decides between competing strategies,” Moita adds. “And moreover, these neurons are of the type that sends motor commands from the brain to the ‘spinal cord’ of the fly. This means that they may be involved not only in the choice, but also in the execution”.

The findings should help provide a starting point for identifying how the brains of other species handle defense, the team explains, as “defensive behaviors are common to all animals”.

The paper “Speed dependent descending control of freezing behavior in Drosophila melanogaster” has been published in the journal Nature.

Meet Chuño, a space worthy food that the Incas made eight centuries ago

The Inca empire once spanned the length of the Andes, and was the largest single country in pre-Columbian America. This is even more impressive when you consider just how incredibly harsh the Andes can be — freezing by night, rugged, dry, and windy all the time. In a time where any type of information or goods had to be transported by human or animal effort, maintaining an empire seems almost impossible.

But the Inca did it. The unique requirements of the Andes led them to develop staple food that rivals modern astronauts’ food in shelf-life, nourishment, and ease of transport to power their way to an empire. That food is called Chuño, and is still being made the same way it has been eight centuries ago — by leaving potatoes out for a few nights.

Black and white Chuño.
Image via yonosoycocinero

Do you want some fries with that?

Chuño is basically freeze-dried potatoes, which is remarkable as they were developed by a culture that had almost zero food-processing technology. What they did have though was a harsh, unforgiving climate, which they put to good use. Altiplano villagers, living in the high plateaus of Bolivia and Peru, make chuño by using the warm days and freezing nights of June to repeatedly freeze and thaw the potatoes, then crushing them underfoot to remove the tubers’ skin and push out the liquids.

For such a simple production process, the result is incredible — Chuño is really filling and it can be stored and eaten for a decade after being prepared with the simplest of storing methods. There’s actually two varieties of the food — black chuño is made with bitter potatoes left to freeze overnight then crushed to remove the liquids inside, until it’s completely dehydrated. White chuño is made by soaking potatoes in the cold rivers and streams of the area, then sun-drying them.

“It was the food that sustained Inca armies,” said Charles C. Mann, an author who has written extensively on the Americas before the European conquest.

The food is little-known outside of the Andes, and newcomers to the region take a little bit of getting used to it. Some have said that it tastes nothing like a potato should, but comes really close to the taste of chalk. Or Styrofoam. Its smell has also been compared to dirty socks. Yum!

So it’s a bit of an acquired taste. Locals still love chuño, though. All you need to do before eating chuño is to rehydrate the potato, but locals cook them into several tasty dishes, usually serving it with an Andean chili called ají. Or they grind them into a flour which they use to thicken soups and stews.

But the most useful thing about chuño is its long shelf life. When the going gets tough and there’s no money for canned foods, or no llamas for meat, and there’s a bad harvest, chuño comes in and saves the day.

“This ability to store food is important in a region where periodic droughts can destroy a year’s crop,” said Clare A. Sammells, an anthropologist who wrote an ode to the often-shunned freeze-dried staple. “Chuño provides the food needed to survive.”

For me, chuño is incredible because it shows just how resourceful humans can be. The Andean people took a look around and said “Ok, what do we have? Deadly cold nights, loads of dust and these here tubers.” Then they used them to make food worthy of space flight. Sock-smelling pieces of chalk-like space food, but no less impressive.