Determination of sleep spindles with time series approach

Year 2025, Volume: 67 Issue: 2, 107 - 124, 24.12.2025

Levent Özbek , Sinan Yetkin , Asuhan Zupan , Hakkı Gökhan İlk , Nihan Nur Ceran Gürlek

https://doi.org/10.33769/aupse.1613459

Abstract

The graphoelements of electroencephalography (EEG), which form the sleep structure, are one of the important research areas of electrophysiology and cognitive science. Sleep structuring is done by experienced sleep experts according to standardized rules. It is performed by visual evaluation according to the graphoelements in the EEG recorded during the night's sleep. This process is subjective, requires time and susceptible for human errors. Among these graphoelements, sleep spindles are the characteristic EEG wave activities. They belong to the non-rapid eye movement (NREM) N2 sleep period. They play a role in sleep structure and cognitive functions. Therefore, it has recently been the subject of research as a clinical determining factor in neuropsychiatric disorders. The initial stage of detection and then further analysis of the waveforms of sleep spindles and the determination of the time and duration of the spindles have gained importance in research. However, since sleep spindles have transient properties compared to background EEG signals, they are difficult to visually analyze. In this study, the sleep EEG was modeled with the time-varying parameter Autoregressive AR (9) to determine the sleep spindles encountered in the sleep EEG. In dynamic linear models given with AR (9), the parameter vector is accepted as a random walk process. Therefore, it can be written as a state space model. By using the adaptive Kalman filter (AKF), the model parameters that can be easily estimated are the time variable parameter and the variance of the white noise process. The focal point of our analysis revealed that the estimated values showed significant changes in the parts with the spindles. We therefore propose that the estimated values of the time varying variance of the white noiseprocess will provide a valuable decision support to sleep experts working in the field of sleep scoring. It can be considered that the method discussed in our study can be combined with existing automatic scoring algorithms and can also be used as a control mechanism in manual scoring for inexperienced sleep scorers.

Keywords

EEG , sleep , sleep spindle , time series , adaptive Kalman filter.

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