Ultrasound machines use high-frequency sound waves to show images of what's inside the human body, like a giant mechanical bat, except with more uncomfortably cold gel. They're not exactly uncommon in the medical world, but most of us associate them purely with things like diagnostic tests and pregnancy exams.

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But ultrasounds can do more than just show bat-magic images of the inside of your body; they can also change the behavior of animals when applied to their skulls. A scientist at the University of Arizona heard about this and decided to try the same thing on humans. Or one human, to be specific: The guy used an ultrasound on his own brain. To his surprise, he experienced an "elevated mood" for an hour afterward. Rather than sitting there with the ultrasound wand to his head giggling for a week or two like most of us would, he decided to get approval to test it on others.

Sure enough, a double-blind study showed that patients with ultrasounded heads reported being in a better mood for about 40 minutes after their skull-wanding. Waving an ultrasound around one's scalp seems to provide humans with the necessary brain-tingles to get us out of a depression slump, at least temporarily.

How Does That Work?

Ultrasounds operate on a similar frequency to that of the structures in the brain that affect mood, which means that putting a bunch of bat-waves into your skull is a bit like turning up a song that your brain really, really likes. Ultrasounds can also focus on really small areas, meaning that they can potentially be used to target and zap particular parts of the brain structure.

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Nicotine, the stimulant drug that occurs naturally in tobacco products, is usually lumped in with the thing people usually do with tobacco products: smoking. Until relatively recently, hardly anyone cared what, if any, benefits nicotine might have, because consuming the stuff was probably going to kill you. It would be like asking whether John Wayne Gacy was a good clown.

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But since nicotine patches were invented in the mid-'80s, nicotine has been gradually losing its psychopomp reputation. More and more scientists have started asking, "Hey, why do people like to smoke so much?" The question gets relevant when you consider that people with depression are twice as likely to smoke as the non-depressed. Are those people depressed because of their brown teeth and future cancer death, or is it that depressed people are using nicotine to self-medicate?

Spoiler: It's probably the latter, because nicotine is just awesome at fighting depression. A 2006 study of depressed non-smokers assigned people either a nicotine patch or a placebo/glorified Band-Aid. Patients who wore the nicotine patch for eight days or longer reported a "significant" decline in depressive symptoms.

How Does That Work?

Turns out nicotine stimulates the part of the brain that regulates mood and increases your levels of dopamine and serotonin. This isn't to say that you should go out and start smoking to fix your sad; brain benefits don't cancel out addiction and dying of lung cancer. But strangely enough, once it's been removed from its tobacco birthplace, nicotine really isn't that addictive. When you take out all the tobacco-y goodness, it's almost impossible to get lab animals addicted to nicotine, no matter how much you push it on them.

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Still, a lot of scientists recommend that people don't rush out and self-medicate with nicotine patches, because the potential long-term health issues haven't been studied enough. But maybe one day soon, a safe nicotine-derived drug will come on the market, and then we can all thank generations of smokers for sacrificing their healthy lungs to science.

If you don't want to wear a patch or get a machine strapped to your forehead, another surprisingly effective depression-puncher is to simply grab your top hat and cane and go for a walk around your neighborhood. People with mild to moderate depression who walked for half an hour six times a week reduced their depressive symptoms by almost 50 percent, making walking about as effective as taking an antidepressant.

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How Does That Work?

Come on, you don't need me to tell you that exercise is good for you. Exercise, even not-exactly-strenuous exercise like walking, stimulates production of norepinephrine, a neurotransmitter that's awesome for mood. It also increases blood flow to the brain and helps nerve cell growth. It's pretty much magic, and it comes with almost no side effects, apart from maybe looking funny when you try to run.

Of course, the issue here is that motivating yourself to exercise is hard enough even when you're physically and psychologically healthy. We all know exercise is good for us, but most of us still don't do enough of it. I mean, it might be cold outside, and there's people out there, and squirrels might look at us funny. And this reluctance gets a hundred times worse when you're depressed and your motivation factory has shut down completely and outsourced its jobs to hating yourself. But hey, you can always try ...

On the surface, making you feel like crap mentally when you've already got sickness to deal with seems like a dick move on your immune system's part, but inflammation is a crucial part of fighting off infection and fixing damage to your body. The sickness behavior it brings with it can actually be an advantage; you're more likely to get better from the flu if you stay in bed and stare at the wall rather than go out to compete in a roller derby. The system only goes wrong when sickness behavior appears without an obvious illness or injury to cause it, and that's when things really start to get weird. There's a theory that a lot of what we call "depression" is actually sickness behavior caused by a source of inflammation that's hiding out in your body somewhere, messing the whole place up like a rotten burrito at the back of a fridge.

You'd expect that if some forms of depression were in fact long-term inflammation in disguise, medical treatments that supercharge the immune system (and therefore cause inflammation) would also cause depression. And you'd be right, smart person! The hepatitis C virus is sometimes treated with injections of a type of cytokine called interferon, which pumps up the patient's immune system. One in four previously non-depressed patients who undergo interferon therapy will develop a major episode of depression as a result of treatment, and some estimates are even higher than that. That's right: If you're lucky enough to be one of the people vulnerable to the psychological effects of a crazily boosted immune system, depression is injectable.

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So if you're currently depressed, and the people around you keep brushing it off and telling you to toughen up, clearly the thing to do is carry an interferon-filled syringe around. The next time someone tells you that depression is "all in your head," jab them in the neck with your syringe and see how they like it.

C. Coville is not responsible for any assault charges that might come as a response to sticking a syringe into people's necks, but can be found on Twitter and Tumblr.