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The way your brain reacts to stimuli might tell us more about who you're friends with, and swatting at mosquitoes might one day bring us positive results.

Hosted by: Hank Green
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Hank: So, I'm doing things in your brain right now, and if that creeps you out, I don't blame you, but the fact is, watching this video is producing certain responses in your brain as you absorb and react to what you're seeing and hearing, and according to new research published this week in the journal Nature Communications, the way your brain lights up as you're watching might have a lot to do with who you're friends with.  

We've known for a while, maybe forever, that the more you have in common with someone, the more likely you are to get along with them.  That's called homophily, which is just a fancy way of saying we tend to like people with similar interests and worldviews.  Of course, that doesn't mean that you can't have a close relationship with someone who's different from you, it's just less common. 

In this week's study, the researchers analyzed similarities between friends in a new way based on their brain activity.  First, they took a group of 279 grad students and mapped out the social network within that group: which people were friends or friends-of-friends and so on, until they figured out how everyone was connected to each other.  Then, they selected 42 people from the group for an fMRI study.  When the neurons in a part of your brain are more active, they need more oxygen, so more blood flows to that area.  With an fMRI scan, you can see that extra blood flow and use it to map out brain activity. 

For this study, the researchers looked at which parts of peoples' brains lit up in response to videos from different genres, like music, comedy, and science.  People experience the world in different ways.  Like, maybe one person will agree that that video of goats yelling like humans is the funniest thing they've ever seen, or they'll whip out their phone and start texting during the best part.  If they're enjoying it, the parts of the brain responsible for those feelings will be flooded with activity and if they're feeling something else or just bored, other areas will be active instead.  

Well, this team found that the closer people were within the social network, the more similar their brain scans were.  In fact, they were able to use those brain scans to accurately predict whether people were friends or friends-of-friends or whatever.  Now, it's hard to know here what's the cause and what's the effect.  You might have a tendency to become friends with people who have similar worldviews.  You and your friends might develop similar perspectives together over time, or it might be some combination of both.  For now, all we know is that your connections to your friends can run pretty deep, to the point where they might actually show up on brain scans.

So without access to an fMRI machine, you can't know exactly how this video or any other video will affect a friend's brain, but just by getting them to watch it, you might be making their brain light up in ways that are similar to yours.

Meanwhile, some things are so universal that everyone agrees, whether they're friends or not, and one of those things is that mosquitoes are the worst.  If you've ever felt like they have a personal vendetta against you, well, you might be right.  That is an actual established scientific thing, but in a study published last week in the journal Current Biology, researchers found that you might be able to change their preferences by swatting at them.

In their experiment, the researchers first trained a bunch of mosquitoes to associate the smell of humans with mechanical shocks and vibrations, things that the insects would want to avoid.  Then, they compared the reactions of trained and untrained mosquitoes to the scent of humans and an odor-less control.  While the regular mosquitoes were, of course, attracted to the delicious scent of humans, the trained mosquitoes lost their attraction to the human scent and treated it just about the same as the control. 

So if you want to get mosquitoes to stop chasing you, it might help to have them associate your smell with something they want to avoid, like your hand whacking them out of the air.  If you think researchers were done after they trained a bunch of tiny insects to avoid certain smells, you would be wrong, because not only did they end up with the beginnings of a mosquito circus like, trained mosquitoes, they also made them costumes.  Helmets, at least, in the form of suction electrodes that stuck them in place while they flew against a stream of air.

While the mosquitoes were stuck in place, the team tested how their responses to the odors of different compounds were effected by extra dopamine, the signaling molecule that controls the feeling of reward.  Mosquitoes that got the extra dopamine tended to show higher levels of brain activity in response to the smells, confirming that it's a big part of how mosquitoes process smells and learn behavior.  The team then went on to genetically engineer mosquitoes in a way that stopped their dopamine receptors from working as well and found that those mosquitoes were really bad at learning to avoid certain scents, which maybe isn't all that surprising, but it's an important building block for future research.

Mosquito-borne illnesses are still a huge problem in many parts of the world.  The World Health Organization estimates that there were over 200 million cases of malaria in 2016 alone.  One way to fight these diseases might be controlling how mosquitoes learn different behaviors like that the smell of humans means delicious blood, and if we want to change what's happening in the brains of mosquitoes, it helps to know more about those processes.  

In the meantime, if you are one of those people that always gets covered in bites, at least you know that your swatting isn't entirely in vain.  You might actually be able to teach those mosquitoes to leave you alone, some of them anyway, and the rest of them, go ahead and kill them.

And if you're interested in learning more about the never-ending mosquito problem, you can check out our episode about what would happen if we killed all the mosquitoes.  Yes, people are thinking about it.  Maybe someday it'll happen.  

Thanks for watching this episode of SciShow News.  It was made possible by our Patreon President of Space, SR Foxley.  Thank you, SR.