Neuroscientists have proven yet again that using a cell phone impairs one’s ability to stick to the yellow line. The authors of the Carnegie Mellon University study, which is upcoming in the journal Brain Research, admit that multitasking in this way “intuitively seems dangerous”—then go on to list 23 behavioral studies that prove even hands-free devices affect driving performance. So what’s the big news? fMRI, my friends. The Carnegie Mellon team is the first to back up the behavioral work with cold, hard brain data, gleaned from 29 study volunteers who engaged in a driving game while listening to chatter and keeping their heads perfectly still in an fMRI scanner tube.

The scientists found that listening reduced the amount of brain power one would otherwise reserve for driving by a whopping 37 percent. To the researchers at least, this was surprising. Talking and driving draw on different areas of the brain and scientists suspected that the areas could work independently on each task. But it turns out “there’s only so much that the brain can do at one time, no matter how different the two tasks are,” says lead investigator Marcel Just.

Armed with this new data, Just testified yesterday at the Pennsylvania House of Representatives Transportation Committee Hearing on Distracted Driver Issues. The committee is debating a bill that would ban handheld phones while driving in that state.

And so it could be that fidgety, bored drivers may soon have no options left to pass the time. Well, none except the radio, the Big Mac and fries, their driving companions, gesticulating to other drivers, and swatting away the cocker spaniel in the back seat.

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