Sleep spindle-related electroencephalograph activity of young adults and its relation to cognitive functions

Abstract

Objective: Sleep spindles are phasic bursts of thalamocortical activity, typically defined as 11-16 Hz (in sigma frequency band) with a duration of 0.5 and 2 seconds. Spindles are most prominent during N2 sleep and are a defining feature of this stage. The aim of the present study was to investigate the association between spindle characteristics and cognitive functions of young adults.

Methods:The study sample consisted of 17 healthy male subjects aged between 19 and 28 years.The participants had no medical or psychological conditions and were not taking any medications that might affect their sleep pattern and neuropsychological measurements. Polysomnography recordings were conducted from 22:30 to 07:00 hour for two subsequent nights. The first night was for adaptation to the laboratory conditions and to rule out sleep apnea syndrome and periodic leg movements. The second night was used to analyze macro and micro parameters of sleep. A neuropsychological test battery comprising the Serial Digit Learning Test, Raven Standard Progressive Matrices, Verbal Fluency Test,Trail Making A-B, and the Auditory Verbal Learning Test were administered before the second-night sleep session. Sleep spindles in all non-rapid eye movement stage 2 sleep were scored visually from C3-A2 electroencephalogram derivation after polysomnographic analysis was completed. Each 30-sec epoch was analyzed with a high-pass band filtered at 0.3 Hz, and a low-pass band filtered at 35 Hz. Spindle characteristics such as duration, amplitude, mean and peak frequencies were analyzed using the fast Fourier transform algorithm. The association between the characteristics of sleep spindles and the neuropsychological test scores were analyzed using Spearman correlations.

Results: Significant positive correlations were found between spindle density and both verbal auditory learning performance and verbal fluency, cognitive flexibility, and semantic organization performances. The serial digit learning test was correlated positively with mean duration, mean frequency, and peak frequency of sleep spindles. Finally, the mean duration, and mean frequency of spindles were positively correlated with verbal fluency, cognitive flexibility, and semantic organization.

Conclusion: The associations between spindle features and memory, verbal fluency, and verbal learning abilities were consistent with previous research findings suggesting that sleep spindles might be related to cognitive abilities and the potential to learn. In other words, it might be an indicator of the current level of aptitude for learning.