In order to function as well as healthy sleepers given memory tests, people with insomnia need to fire up more neurons, researchers here said.

They compared working memory in 12 adults with chronic insomnia to working memory in nine healthy controls and found little difference in responses, except that functional MRI revealed a higher level of brain activation in the patients with insomnia, said Henry Orff, M.S., a doctoral student in psychology at the University of California San Diego, who reported the findings at the annual meeting of the Associated Professional Sleep Societies.

"On most high-order tasks, we're not seeing much difference," he said, noting that most studies simply measure whether the subject can perform the task, not how hard it was to perform the task. Studying brain activation can help show that difficulty, he said. "We find that it takes more neurophysiological effort to perform the same task."

And while the insomnia patients' brains appeared to be working harder, they were also working faster, as they gave correct responses significantly faster than controls (P=0.001), Orff said.

Brain activation data may be the missing link that explains why, in several studies, people with insomnia often perform complex tasks as well as healthy sleepers, Orff said.

The study involved 12 people with primary chronic insomnia, six men and six women, average age 40, as well as nine matched healthy sleepers, five men and four women, average age 36.

The investigators used the N-Back test to assess the subjects' working memory, as well as a verbal learning test and a memorization test. The N-Back test requires that an individual listen to a series of letters and push a buzzer when a letter is said that is a repeat of a letter said previously a specific number of times.

In the 2-Back test, the individual responds when a letter is repeated that was said two letters previously. In the 3-Back test, the repeat is of a letter said three letters previously. The N-Back test was conducted while the patient was undergoing functional magnetic resonance imaging (fMRI).

The investigators compared the group's fMRI Blood Oxygen-Level Dependent (BOLD) activation during the 3-Back condition.

The team selected regions in which the groups showed significant differences in cerebral activation. BOLD activation is conventionally measured in fMRI as a way of detecting the areas of the brain that are activated and the level of activation.

The investigators also measured the subjects' behavioral performance by the reaction time they needed to give correct responses, the number of correct responses, and the number of errors.

Compared with healthy sleepers, the people with insomnia showed increased BOLD activation in the right middle front gyrus and the anterior right middle frontal gyrus. Those areas are involved in visual-spatial attention and the coordination of cognitive processes, Orff said.

People with insomnia also showed less activation than healthy sleepers in the right middle occipital gyrus and the fusiform gyrus, as well as the left motor cingulate and postcentral gyrus. These areas of the brain are involved in visual and motor processes. Orff theorized that the baseline activation in these areas might already be higher than that of healthy sleepers.