STUDY OBJECTIVES

To examine the joint effect of insomnia and objective short sleep duration on neuropsychological performance.

DESIGN

Representative cross-sectional study.

SETTING

Sleep laboratory.

PARTICIPANTS

1,741 men and women randomly selected from central Pennsylvania.

INTERVENTIONS

None.

MEASUREMENTS

Insomnia (n = 116) was defined by a complaint of insomnia with a duration > or = 1 year and the absence of sleep disordered breathing (SDB), while normal sleep (n = 562) was defined as the absence of insomnia, excessive daytime sleepiness, and SDB. Both groups were split according to polysomnographic sleep duration into 2 categories: > or = 6 h of sleep ("normal sleep duration") and < 6 h of sleep ("short sleep duration"). We compared the groups' performance on a comprehensive neuropsychological battery that measured processing speed, attention, visual memory, and verbal fluency, while controlling for age, race, gender, education, body mass index, and physical and mental health.

RESULTS

No significant differences were detected between insomniacs and controls. However, the insomnia with short sleep duration group compared to the control with normal or short sleep duration groups showed poorer neuropsychological performance in variables such as processing speed, set-switching attention, and number of visual memory errors and omissions. In contrast, the insomnia with normal sleep duration group showed no significant deficits.

CONCLUSIONS

Insomnia with objective short sleep duration is associated with deficits in set-switching attentional abilities, a key component of the "executive control of attention." These findings suggest that objective sleep duration may predict the severity of chronic insomnia, including its effect on neurocognitive function.