medwireNews: Researchers have found abnormal neural function in patients with primary insomnia, which may help explain why these patients find it hard to concentrate on daytime tasks despite the absence of objectively measured cognitive deficits.
Magnetic resonance imaging showed that patients with insomnia had reduced activation in brain regions needed to carry out a working memory task, and impaired deactivation in “mind-wandering” default regions not normally used during task-focused behaviors.
This was despite insomnia patients and good sleepers performing equally well on the N-back task, the researchers note.
“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,” lead researcher Sean Drummond (VA San Diego Healthcare System, California, USA) told the press.
He added that the findings also show that “some aspects of insomnia are as much of a daytime problem as a nighttime problem. These daytime problems are associated with organic, measureable abnormalities of brain activity, giving us a biological marker for treatment success.”
A total of 25 patients with moderately severe insomnia and 25 good sleepers participated in the study.
The good sleepers showed significant positive activation in 16 of 18 areas of the brain known to be related to the N-back task. These regions included widespread areas within the frontoparietal working memory network, motor and visual processing regions, thalamus, and cerebellum.
By contrast, significant positive activation was seen in only four of the 18 areas in patients with insomnia. For 10 of the other areas, there was no significant activation, and for the remaining four there was negative activation.
The brain responses of patients with insomnia also differed to those of good sleepers with increasing task difficulty. In good sleepers, cerebral responses in the right dorsolateral prefrontal cortex and classic working memory areas increased, whereas there was no modulation of cerebral responses in patients with insomnia.
Also, as the task got harder, good sleepers deactivated those areas of the brain not normally needed for task-focused behaviors, whereas insomnia patients were less adept at disengaging these regions, and reported being less able to concentrate and feeling more sleepy.
These subjective responses “may manifest as the subjective cognitive complaints so common in [primary insomnia],” the team writes in Sleep.
In a related commentary, Michael Chee (Duke-NUS Graduate Medical School, Singapore) says the results are “unique as well as enigmatic.”
He agrees with Drummond et al that the reduced task-related responses in insomnia patients may reflect a “fundamental change in brain physiology,” with baseline cerebral blood flow increased in response to the effects of hyperarousal.
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