In "new" Gmail, when you compose a new email, the "send" button is displayed prominently in the upper left (sometimes in a bright color, depending on which theme you're using). But when you respond to a conversation already in progress, the button in the place of the "send" button brings you back to your inbox.

It's a small but subtle change from the old version, and one that's led me more than a few times to go back to my inbox instead of sending an email. Or think about every time Twitter changes its design, or Facebook moves things around in your news feed — where did Events go? — or when your favorite website redesigns its homepage and you "can't find anything" anymore.

According to a new study in the journal Cognitive, Affective, & Behavioral Neuroscience by Jason Moser, Hans Schroder and others at Michigan State, that's because our brains have a finite capacity for processing information — and when rules, or designs, change, we mess up. It doesn't matter, it seems, if the new rules of a design are intended to make things easier for us — our brains will still have trouble processing the change no matter what. Which is why you see people getting so agitated when new versions of an OS move their trash can.

The study authors focused on one area of the brain, the anterior singular cortex, which is responsible for monitoring our actions — like which mouse button to press. "When you switch the rules on people, this part of the brain has to go into overdrive to suppress the old rule and remind itself that this is the new rule," says Moser. "The cost of that part of the brain going into overdrive is it pays less attention."

For the study, 67 undergrads did a computer task that was easy to mess up: they were shown letter strings and told to press a specific button — left or right — depending on which letter was in the middle (M or N). After 50 trials, the rules was reversed: they had to press the opposite button depending on which letter, M or N, was in the middle. They made more consecutive errors after the rules were reversed, and the study authors concluded that "when the rules are reversed, our brain works harder to juggle the two rules... When we spend brain energy juggling two rules, we have less brain power available for recognizing our mistakes."

So what's the solution? Moser — who also studies anxiety — says that he encourages people to "focus as much as possible on what they're doing in the moment. They should acknowledge a freakout, or anxious thoughts, that come, and focus on the task they're into." He adds that even though some people are better multitaskers than others, everyone can benefit by allowing themselves chunks of time to "offload as much stuff as possible — give yourself some time of pure focus."

Or you could also just revert to the design you're familiar with. This Gmail hack is a little convoluted, but will restore much of the design and functionality of "old" Gmail. I'll never hit "inbox" when I mean to hit "send" — while simultaneously Gchatting, looking at Twitter, and writing this article — ever again.