The memory benefits of distraction

Most people take it as a given that distraction is bad for — oh, hey, a squirrel!

Where was I?

… Right. Most people take it as a given that distraction is bad for memory. And most of the time, it is. But under certain conditions, the right kind of distraction might actually help you remember.

Nathan Cashdollar of University College London and colleagues were looking at the effects of distraction on memory in memory-impaired patients. They were specifically looking at distractions that were totally off-topic from a particular task, and how those distractions affected memory performance. Their results were published November 27 in the Journal of Neuroscience.

The researchers worked with a small group of people with severe epilepsy who had lesions in the hippocampus, and therefore had memory problems. They compared them to groups of people with epilepsy without lesions, young healthy people, and older healthy people that were matched to the epilepsy group. Each of the participants went through a memory task called “delayed match-to-sample.” For this task, participants are given a set of samples or pictures, usually things like nature scenes. Then there’s a delay, from one second at the beginning of the test on up to nearly a minute. Then participants are shown another nature scene. Is it one they have seen before? Yes or no?

The task starts out simply, with only one nature scene to match, but soon becomes harder, with up to five pictures to remember, and a five-second delay. People with memory impairments did a lot worse when they had more items to remember (called high cognitive load), falling off very steeply in their performance. Normal controls did better, still remaining fairly accurate, but making mistakes once in a while.

Then the scientists introduced a distractor. During the delay between the samples and the potential match, participants saw a different image, a neutral face. The controls showed no change in their accuracy. But the group with memory problems, rather than being the worse for the distraction, turned out for the better. In fact, they improved so much that there were no longer different from healthy controls.

The healthy controls didn’t show differences in performance with a distractor when they had more items to remember. But maybe the task wasn’t hard enough. The scientists showed that even healthy controls will have worse performance if you give them five items to remember and an even longer delay of 45 seconds. Again, when the participants got the distracting face, their performance improved.

How could this work? The scientists decided to look at theta rhythms in the brain. Theta rhythms are a type of oscillation, waves of voltage changes, representing many neurons acting together. The brain waves follow certain frequencies. Thetas, for example, are on a frequency of 4 to 7 hertz. Theta rhythms have been associated with learning and memory and can be detected when someone is “rehearsing” a memory, trying to remember something for later.

In control participants who weren’t doing a difficult task, theta rhythms decreased during the delay between the trial and the test sample. However, in the group of patients with memory impairments — for whom the task was very difficult and who had to “rehearse” more — their theta rhythms increased during the delay period. When presented with a distraction, however, the memory-impaired patients had their theta rhythms broken up by the distraction. They could no longer “rehearse” the memory. This break in rehearsal was associated with increased memory performance.

So distracting yourself from “rehearsing” may help you remember when you have a lot on your mind. It also makes us question why this is the case. Is the increase in theta bands really an increase in “rehearsing?” What neuronal activity does it reflect? Why are those theta bands unhelpful in people under high memory pressure? Shouldn’t extra “rehearsing” help your performance? Why doesn’t it? In addition, this is only one type of memory task, and only one type of distractor. It would be interesting to see if the results translate to other memory tasks and other types of distraction, a sound or a conversation, for example. But it does highlight one situation where distraction — check out this exploding whale! — might help memory, instead of making it worse.