The first time I heard that shooting electrical currents across your brain can boost learning, I thought it was a joke. The Conversation

But evidence is mounting. According to a handful of studies, transcranial direct current stimulation (tDCS), the poster child of brain stimulation, is a bona fide cognitive booster: By directly tinkering with the brain’s electrical field, some research has found that tDCS enhances creativity, bolsters spatial and math learning and even language aquisition – sometimes weeks after the initial zap.

For those eager to give their own brains a boost, this is good news. Various communities have sprung up to share tips and tricks on how to test the technique on themselves, often using self-rigged stimulators powered by 9-volt batteries.

Scientists and brain enthusiasts aren’t the only people interested. The military has also been eager to support projects involving brain stimulation with the hope that the technology could one day be used to help soldiers suffering from combat-induced memory loss.

But here’s the catch: The end results are inconsistent at best. While some people swear by the positive effects anecdotally, others report nothing but a nasty scalp burn from the electrodes.

In a meta-analysis covering over 20 studies, a team from Australia found no significant effects of tDCS on memory. Similar disparities pop up for other brain stimulation techniques. It’s not that brain stimulation isn’t doing anything – it just doesn’t seem to be doing something consistently across a diverse population. So what gives?

It looks like timing is everything.