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Spend five minutes in any forest and you'll probably hear birds chirping.  It's a kind of vocal communication, which are sounds animals make with their mouth and throat parts like talking, roaring, or meowing, and there are tons of papers out there about birdsong and how it can mean anything from look how cool my feathers are to run away, but about 150 years ago, Charles Darwin had a thought: what if the non-vocal sounds that birds make, like by flapping their wings, mean something too?  

Scientists have been looking into this question for a while, and this week, a study from the Australian National University seems to give more evidence that Darwin was right.  If you've spent any time on mainland Australia, you'll have heard the crested pigeon whistle, except it isn't a mouth sound.  They whistle when they flap their wings, which got them the nickname whistle-winged pigeons, say that five times fast.

In a 2009 paper, researchers had noticed something important: other pigeons seemed to react to the whistles.  So a group of biologists, including one of the previous papers' authors, wanted to do more tests to see if the noise actually communicated something.  In the 2009 research, they measured crested pigeon wing feathers and discovered a weirdly thin one, specifically the eighth primary feather.  Measurements in both studies showed that the pigeons produced two distinct notes as their wings flap and vibrate the feathers.  One is much higher than the other.  Also, when the birds were flying away in a hurry, they flapped faster and the sound was louder.

So the researchers carefully removed the weird feather from some birds, all in the name of science, but it's okay, they grow back.  Without the narrow feather, the highest note disappeared, and wind tunnel experiments confirmed that the feather makes the noise when it's vibrating on its own.  Most importantly, the researchers compared the reaction of other crested pigeons to recordings of birds flying away with and without the special feather, and there was a clear difference.  When the other birds heard the high-pitched sound, they were more likely to get out of there in a hurry as if there were an alarm blaring, but if they heard the recordings without that alarm, they were more likely to stick around or take off more leisurely.

This gives some solid evidence for Darwin's non-verbal communication idea showing how the sound is produced and how other birds respond to it, and the researchers say it makes sense evolutionarily, too.  These pigeons are always gonna make a sound if there's danger nearby, so more birds know to escape and stay alive, unless a scientist comes along and takes away some of their feathers.

But enough about birds, let's talk about humans, because if you're a student, a parent, or really anyone, you've probably been sleep-deprived before.  You feel sluggish, like your mind is swimming through fog to make decisions, and everything just seems harder, and this week, researchers from UCLA took a deep look into the biology behind this feeling.  When you're tired, your neurons sort of go to sleep, too.

In a paper published in the journal Nature Medicine, this team of neuroscientists monitored the brain activity of 12 patients who had electrodes in their heads, but before you get too weirded out by that, the patients were already in the hospital to get treatment for epilepsy.  Epilepsy is a super broad term for abnormal brain activity that causes seizures.  There's a lot of variation in causes and symptoms, which means treatments can vary a lot, too.  Sometimes it's hard to pinpoint the exact brain region that's affected, so doctors can implant electrodes to keep track of the electrical signals throughout the brain when a seizure happens, and this can help doctors decide if brain surgery is worth the risk to remove something that might be causing the seizures, like scar tissue, and when doctors want to cause a seizure in a controlled hospital setting, sleep deprivation is key. 

Electrical activity in the brain changes when you're asleep or awake, so messing with that cycle can influence seizures.  This worked out well for these researchers, too.  They had a group of probably bored, sleep-deprived people with their brain signals being monitored, so they can see what happens to neurons when we force ourselves to stay awake.  At different times, the patients were given a set of images to categorize as quickly as they could, while the researchers monitored brain activity in a region called the temporal lobe.

Among other things, the temporal lobe translates sensory information into conscious thought, basically information processing, like if I see a roundish red thing with a brown stem on top, my temporal lobe helps me recognize that it's an apple.  The scientists noticed that the neurons in the temporal lobe actually fired more slowly and passed along weaker signals as they patients did this task after staying awake longer.

The researchers also measured brainwaves, the repeating cycles of many neurons firing, and these brainwaves slowed down in certain regions, too, so they kind of looked like the ones linked with sleep.  We've known for a long time that sleep deprivation can mess with how you act, but this is the first study in humans that might explain what's going on biologically.

The researchers say the effects of these basically sleeping neurons are similar to being drunk, which has huge implications for things like driving.  Like, it's going to take longer for your brain to process an unexpected pedestrian on the road and react, so that's maybe something to think about next time you're watching Netflix until 3AM.  

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