Objective sleep duration is associated with cognitive deficits in primary insomnia: BDNF may play a role

Objective sleep duration has been linked to insomnia severity. However, cognitive functions of people with insomnia with different sleep durations have been seldom addressed. Brain-derived neurotrophic factor (BDNF) has an important role in cognitive function and has been linked to clinical insomnia recently. The present study aimed to evaluate the comprehensive cognitive functions in people with primary insomnia with different objective sleep durations, and further examine the involvement of peripheral BDNF.

Fifty-seven people with insomnia were subdivided into short sleep duration (SSD, sleep time < 6 hr) group and normal sleep duration (NSD, sleep time ≥ 6 hr) group based on polysomnography data. Twenty-nine healthy controls (HC) were matched on age, gender, and education. Cognitive function was assessed using a comprehensive and sensitive neuropsychological test battery. Both objective and subjective insomnia statuses were estimated. Serum BDNF level was measured using enzyme-linked immune sorbent assay.

Compared with HC, the SSD group showed impaired neuropsychological performances in spatial span, brief visuospatial memory test, fluency, managing emotions, and continuous performance tests. In contrast, NSD had bad performance only in brief visuospatial memory test and continuous performance tests, and relatively better than SSD group in the latter test. People with SSD insomnia but not NSD had decreased BDNF levels compared with HC, and neuropsychological performance was positively correlated with BDNF levels only in SSD group.

Primary insomnia was associated with impaired neuropsychological performance, and the impairment might be related to decreased objective sleep duration. In addition, decreased peripheral BDNF might mediate the impaired cognitive functions of people with insomnia with SSD.