Exploring The Change Of Brain Oscillation During Post-learning Sleep:Based On An EEG Signal

Objective: Sleep is a greatly important physiological state in mammals and sleep can save energy,enhance immunity,promote metabolism and restore physical strength.Now increasing number of researches focus on the relationship between sleep and memory.It is well-known for us that sleep can promote memory consolidation and keep the memory preserving for a long time.Different sleep stages involved in different types of memory processing.Some studies found that learning-related increases in spindle number and amplitude have been observed in the human EEG.Our study aimed to provide further evidence for the role of the specific oscillations during sleep in memory process.Methods: We recruited thirty-three college students aged 18-28 years old and they all had normal sleep-wake cycle.Our study was a balanced crossover design and the aim of the current study was to investigate experience-dependent changes in nocturnal sleep EEG activity after learning images without emotional tone.All participants need to sleep in the experimental environment two nights.The first night was a control night and they did not need to learn anything.At the second night,subjects were asked to learn some neutral images before went to bed.Then an hour before their habitual bedtime,we hook up the electrodes.After lights off,subjects were allowed to sleep for 8h.The whole night sleep EEG recordings were subjected to spectral analysis using a fast Fourier transform.In addition,for the detection and analysis of sleep spindle,we use a fast time frequency transform to analyze instantaneous amplitude,frequency and bandwidth.Paired sample t tests corrected were used for spectral power,sleep spindle data.Results: We found that there was no statistically difference in sleep structure between learning night and baseline including sleep latency,total sleep time,sleep efficiency,N1%,N2%,N3%,and REM%(all P> 0.05);Compared with the baseline,the density of spindle in NREM sleep increased after learning materials before sleep(P = 0.009),while we did not found significant difference statistically in the count(P = 0.465),duration(P = 0.249)and amplitude of the spindle(P = 0.074)between two nights.Meanwhile,the count(P = 0.795),density(P = 0.116),duration(P = 0.190),and amplitude(P = 0.777)of slow oscillation in NREM sleep did not increase during a post-learning sleep.During the slow wave sleep,the count of SO-spindle coupling increased in learning night compare with the baseline(P = 0.011).No difference could be found in N2 sleep(P = 0.092).During REM sleep,there was no statistical difference in theta energy(P = 0.063)and density(P = 0.068)between learning night and not learning night.Furthermore,we found positive correlations between the count of spindle and memory performance(P = 0.029).Conclusion: Sleep spindle and the coupling of sleep spindle and slow oscillation are important mechanisms of memory consolidation during sleep.