Some people with insomnia may have trouble activating certain brain regions involved in short-term memory, a new study suggests.

In addition, people with insomnia may have problems turning off brain regions that are typically active when the mind wanders, the study found.

The findings may explain why people with insomnia often say they struggle to concentrate during the day or complete tasks.

"Based on these results, it is not surprising that someone with insomnia would feel like they are working harder to do the same job as a healthy sleeper," study researcher Sean Drummond, an associate professor of psychiatry at the University of California, San Diego, said in a statement. [7 Strange Facts About Insomnia]

But despite these brain differences, people in the study who had insomnia preformed just as well on tasks involving short-term memory as those people without sleep problems.

Working memory differences

The study involved 25 people with primary insomnia, meaning they have difficulty sleeping but do not have other related conditions, such as mental health problems. Another 25 people without sleep problems were also included.

During overnight sleep tests, participants with insomnia slept an average of six hours a night, while those without insomnia slept an average of seven hours.

All participants completed a working memory task while they had their brains scanned using functional magnetic resonance imaging (fMRI). Working memory is the ability to process and store short-term information in the brain, which can then be used to complete a task at hand. In this study, the working memory task involved viewing a series of letters and identifying which ones had been displayed recently (specifically: one, two or three letters ago).

During the task, people with insomnia showed less activity in brain regions involved in working memory, compared to people without the sleep problem.

As the task got harder, participations without insomnia began showing more activity in another brain region also involved in working memory, the dorsolateral prefrontal cortex. However, this region showed now change in people with insomnia.

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In addition, as the task became more difficult, people without insomnia turned off regions involved in the brain's "default mode." These regions are active when a person isn't focused on anything in particular (as in when the mind wanders). However, people with insomnia did not turn off these regions.

More than trouble sleeping

"The data help us understand that people with insomnia not only have trouble sleeping at night, but their brains are not functioning as efficiently during the day," Drummond said.

Because the study included only people in whom insomnia was the primary condition, future studies are needed to see if the results apply to people who have other, related conditions along with insomnia.

In addition, the study involved people with moderate insomnia, and so it is not clear if the results apply to people with more severe forms of the disorder, the researchers said.

The study is published in the September issue of the journal Sleep.

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