This Is How Spending A Lot Of Time Alone Can Literally Change Your Brain

This one makes perfect sense from an evolutionary perspective. A 2015 study found that people who spend a lot of time alone are very good at detecting threats in their environment and are sensitive to potential signals that something's wrong. The reason? Humans have usually existed in family groups that protected each other from threats and worked together to defend themselves. If you're on your own, your brain switches to a more vigilant mode because nobody's around to watch your back in case, say, a wild animal is about to eat you. It's probably not a good idea to watch a lot of horror movies when you're spending time on your own, though, or you'll never stop looking over your shoulder.

A new study shows that, in people who are chronically socially isolated, a neurochemical called tachykinin might mean they feel more aggressive in general. Grumpiness and irritability, according to this study, aren't just because you've been away for a while and now find your friends irritating; they're a psychological change brought about by brain chemistry. Socially isolated flies and mice both showed increases in tachykinin that made them more aggressive and fearful of others, so don't be surprised if coming back into social life after some time away means you feel moodier and less tolerant than usual. It's just your neurons readjusting.

Fascinatingly, a study in 2016 found that the brains of people with different genders have different reactions to social isolation, and that being a woman may mean a more intense response. The study looked at mice, and found that while male mice brains tended to react to isolation by chilling out, female mice brains found being alone a bit stressful and started producing a hormone called corticosterone, which is a reaction to really high-stress situations. We're not sure if this is replicated in humans, but if you appear to feel more stressed out by time alone than your male friends, it's possibly neurochemical in origin.

A 2012 study found that mice who are isolated for a long time don't produce as much myelin, a crucial part of brain structure. Myelin is what makes up the protective "sheath" around your nerves, but you might know it as "white matter," as opposed to "gray matter," which comprises the nerve cells themselves. According to the study, a bit of social isolation dipped myelin levels, but didn't result in any different behavior, while spending a lot of time alone meant myelin levels dropped off quite a lot. Less myelin means your brain's signaling ability changes. This is probably why being alone for long periods actually changes our behavior — because our brains are communicating in different, possibly less effective ways.

A study in 2009 was the first to actually look at MRI scans of self-described lonely peoples' brains, and found that a series of different "firing patterns" — neurological patterns of electrical activity in the brain — show up when you're lonely and indicate that you're seeking happiness in ways that aren't social. Lonely people showed far less activity in their temporoparietal junction, a part of the brain that's linked to the perceptions of others, and researchers think that indicates that when you're happy as an isolated person, it's coming from something other than social interactions — like chilling in a bath or playing some awesome music on your own.

A set of studies in 2016 have shown that after periods of social isolation, your brain starts to kick in and demand that you go and talk to somebody. The studies looked at dopamine, a chemical associated with positive feedback, in mice, and found that when they were alone, dopamine signals started to encourage them to seek out social contact, and rewarded them with a flood of happy feelings when they finally found some other mice to play with. This explains the craving for social interaction you may get after some time alone: It's your brain deciding that it's time you got outside, and giving you a massive hit of good feelings when you do.

There are a few seriously positive benefits to time alone, but this one is top of the list: Harvard scientists discovered that when you form memories on your own, they tend to be stronger and longer-lasting than if you'd experienced the same thing with other people. Our brains, it seems, realize that we can't rely on others to remember vital information when we're experiencing them on our own, and so emphasize more accurate storage and recall. This is why studying on your own is often a good idea, and why you may remember those solo holidays much better than you do those group voyages in college (though there could be vodka-related reasons for that).

Overall, a bit of time alone isn't necessarily a bad idea. It gives us recharge time, and makes us appreciate our friends and family that bit more. But don't be surprised if longer-term isolation makes you feel like a different person — because, on several neurological levels, you really have changed.