Next to the many amazing feats our brain pulls off daily, its inferior ability to juggle a few simple tasks sticks out like a sore thumb. Now research from Vanderbilt University suggests that these limits on multitasking arise from slow processing in the prefrontal cortex, the brain’s central executive. Although the area has been known to be involved in multitasking, its exact role is a matter of debate.

Using functional MRI, the researchers found that when people were juggling two assignments, their prefrontal cortex appeared to deal with the tasks one by one—creating that familiar mental bottleneck—instead of processing them in parallel as do sensory and motor parts of the brain. With training the prefrontal activation time became shorter, cranking up the speed of the mental conveyor belt by about 10 times. Unfortunately, the researchers note, the benefits of training might not apply to tasks other than those specifically practiced. “It’s not like you become able to multitask [with drills]; it’s just that you become able to do each task very quickly,” says cognitive neuroscientist Paul Dux, now at the University of Queensland in Australia, who conducted the experiment.