Despite how much noise pop psychology makes about being left-brained or right-brained, the brain is really a very cohesive unit. The right and left hemispheres have some differences, but they communicate with each other via dedicated neural connections that bridge the two halves of the brain.

Some people, though, have the two halves of their brains separated as a treatment for severe epilepsy. What’s remarkable is that this has fewer effects than you might imagine. Although there certainly are differences in how a split brain behaves, people who have this surgery tend to behave largely as we'd expect anyone else to, and they're actually better at certain kinds of dual tasks.

These split-brained individuals are interesting because they can help us understand how the brain processes information and how it integrates or separates tasks that are running concurrently. For instance, we know that the two hemispheres in a split brain have to process tasks separately from each other (the connection between them is gone, remember), with each hemisphere unaware of what the other one is up to.

A group of neuroscientists at the University of Wisconsin-Madison suspected that healthy brains might sometimes process tasks separately when they multitask. Although the brain wouldn't literally split, the researchers thought they might be able to detect two separate networks operating independently of each other.

To test this, the researchers devised a functional magnetic resonance imaging (fMRI) experiment that involved multitasking. They chose listening and driving as the tasks, partly because they’re everyday activities, which means there's less of a chance of just finding an artificial effect in a weird lab task. Another reason for the choice is that we already have an understanding of the networks we use for the auditory and linguistic processing, as well as the networks that are used for the visual and motor processes of driving.

What the researchers wanted to see was whether they could find evidence of the two networks for listening and driving working together at times and separately at other times, depending on the task.

The driving simulation that the researchers used was pretty simple: all the subjects had to do was drive on a two-lane road with no junctions or other vehicles. The complication came in with the additional tasks they had to perform. In the “integrated” task, the drivers had to listen to GPS-like instructions while they were driving, telling them when to change lanes. That’s multitasking, but the two separate tasks have a single aim, which is to navigate the simulation correctly. In the “split” task, they changed lanes at designated objects (like road signs) and listened to the radio, which obviously had nothing to do with the main task of driving.

There are some obvious potential pitfalls here. For instance, GPS voices and radio often sound pretty different. To get around this, the researchers used the same voice to read out both instructions for the GPS task and articles for the radio. They also asked participants about how difficult the tasks were and how drowsy they felt, ultimately testing their driving performance and listening comprehension. All of the checks suggested that the tasks were essentially the same in these respects.

When the drivers were doing the integrated task, the activation in their brains showed an integrated network: their brains were processing both challenges as a single task. But when they were doing the split task, the scans showed less connectivity between the two activity networks. “A brain may functionally split into two separate 'driving' and 'listening' systems when the listening task is unrelated to concurrent driving,” the authors write.

The ability to manage these different networks was also related to driving performance, which the researchers defined as driving in a straighter line with less weaving away from the centerline. If drivers could switch easily between high and low information integration, they were better drivers in both the integrated and the split tasks.

As with many fMRI studies, the sample size in the experiment was small: only 13 male participants. This creates the risk of finding an exciting effect just because there aren’t enough people to even out individual differences. If a different 13 people were used, the same effect might not appear. “I’d definitely like to see it replicated in a larger sample size that includes participants not limited to male adults,” says Gagan Wig, who studies the organization of brain networks and wasn’t involved with this research. “But this is at least evidence that there are some innovative ways of pursuing these ideas.”

The interesting thing about this research, says Wig, is that it shows just how flexible and dynamic the brain is. It’s capable of running concurrent, split networks, but it can also integrate those networks when it needs to. This kind of flexibility has been suspected, he says, but this research has found new ways to detect the integration and separation.

This research leads to further questions. The brain has lots of processing capabilities beyond the ones tested here, and we don’t know which other systems can integrate with one another and which systems can’t. There's also a deeper level to investigate: what sub-networks control the brain's switches between network integration and separation? This is an interesting proof of concept, but there's always more work to be done.

PNAS, 2016. DOI: 10.1073/pnas.1613200113 (About DOIs).