People around the world are strapping batteries to their heads to supercharge their brains.

Seriously. This is a thing.

It's called transcranial direct-current stimulation, or tDCS, and it involves using electric currents to stimulate your brain. The companies that want to sell you tDCS devices claim that it has all kinds of benefits:. They might say that it'll boost your memory and focus.

Some even claim that it can do everything from treat depression to help you sleep better. If that sounds too good to be true — it is. Ah, the truth is a lot more complicated.

Studies have found that tDCS might help with some things. But there's also plenty of controversy about it among scientists, and the jury's still out on how exactly tDCS affects the brain. Even though it involves electric currents, tDCS is a lot less intense than the kind of supercharged electric shocks used in electroconvulsive therapy.

That's the more famous electricity-related therapy that's sometimes used to treat things like really severe depression. A tDCS headset contains two electrodes, called the anode and cathode. The idea is that the anode will boost the area of the brain beneath it, whereas the cathode will inhibit the area beneath it.

The choice of those areas, of course, depends on the particular functions you're looking to play with. Once everything's in place, a small electrical current of around 0.5 to 2.0 milliamps is sent through the electrodes, right into your head. Since the current is so small, it's not painful — as long as you set it up properly.

The most people tend to feel from this kind of current is a mild tingling sensation on their scalp. A tDCS session typically lasts around 20 to 30 minutes, and people usually do a number of sessions over the course of a few weeks. The thing is, most people doing this at home might be making their scalps tingle for nothing, because we still aren't sure if tDCS actually does a lot of the things companies selling these devices are claiming.

Entering the world of tDCS experimentation has a pretty low bar, since headsets are fairly inexpensive. Unfortunately, that's made the literature a little ... messy. One problem is that we still aren't totally clear on what tDCS does to the brain on a physiological level.

We do know that current can affect the way neurons fire, and researchers think that the mild current from the electrodes changes the membrane potentials of neurons, allowing them to fire more easily. The idea is that, with enough stimulation and repeated exposure, the neurons that are getting the stimulation will start firing more. Over time, that might nudge damaged or underperforming brain areas toward functioning in a healthier way all by themselves.

But this is all still the subject of some debate. One study, published in 2016, used a cadaver to measure how much current from tDCS managed to travel through the skull to the brain. Electrodes placed on the inside of the skull showed that around 90% of the electricity applied through tDCS didn't get through at all.

That study raised a few eyebrows, but according to a lot of tDCS experts, the findings actually make sense, since live tissue is better at conducting electricity. Plus, there's a lot of evidence that tDCS affects brain function, so there must be some amount of current – however small – making it through. Which brings us to the other main problem when it comes to t

DCS: we still don't know exactly what effects it has. A lot of tDCS studies are small, pilot studies that need to be replicated before we can draw any conclusions from their results. And some aren't so tight in the methodology department. In meta-analyses that look at results across multiple tDCS studies, researchers have pointed out that the methods used in different studies are so inconsistent that it can be hard to compare them.

There is some well-designed tDCS research out there, though, and based on those studies, researchers have found that it might be an effective treatment for mood disorders, psychosis, and dementia. It might even help people recover from strokes. A 2016 meta-analysis of 17 studies found that stroke patients who did tDCS treatments regained more motor function than patients in the control groups, who did fake tDCS treatments.

Scientists are also looking into tDCS as an alternative treatment for depression. A meta-analysis of data from six randomised control trials, with 289 patients in all, showed that tDCS relieved symptoms of depression, even in people who'd felt no benefits from medication. But that's the thing — researchers are still looking into all this. tDCS seems like it could be really promising, but there's a lot we still don't know.

Sure, some studies have found that tDCS helps stroke patients recover their motor function, but that doesn't necessarily mean that it'll give healthy people better motor function in general. Plus, these studies are done in a clinical setting, which is totally different from buying a device and giving yourself a tDCS treatment at home. If you put the electrodes just a couple of centimeters off from the right spot, or the current is slightly lower or higher than it should be, you might end up stimulating your brain in a way that's completely different from what you wanted.

So, there is some solid evidence that seems to point to tDCS being a useful therapeutic tool in the future. Just … maybe don't run electric currents through your brain on your own until we know a little more. 　 Or do, I'm not your dad. But I will tell you that for the cost of your average tDCS device you could become a significant.

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