Physiology-Based Modeling of Sleep and Wake Phenomena in the Human Brain

Abstract

The brain is a complex system with connections of interacting subsystems, feedback loops operating at different timescales. In this thesis, the focus is on the brain dynamics of sleep-wake states and related phenomena. A general overview of the thesis is given in Ch. 1, to provide the physiological background of the relevant brain dynamics, the electrical activity of the brain, and the phenomena of the circadian rhythm. The corticothalamic neural field model successfully explains different sleep-wake stages. The circadian pacemaker model successfully describes the circadian rhythm modulated by light exposure. Chapter 2 discusses two electroencephalography (EEG) phenomena: (a) spontaneous K-complexes (KCs) with spindles and (b) the evoked response potential (ERP). It is shown here that both KCs and ERPs can be unified within a common theoretical framework. Chapter 3 presents the model ERPs within the overall corticothalamic stability zone in a reduced three-dimensional parameter space for normal (near critical) states, and far from the critical states using the same model presented in Ch. 2. Both theoretical time series and wavelet transform are used to characterize model ERPs. In Ch. 4, a basic circadian model is improved to account for the effects of the different light spectrum and the spectral sensitivity function of the eyes. The model results also are shown to reproduce the circadian phase responses as found in the experiments. This thesis is summarized in Ch. 5 which suggests an overall framework for the two physiology-based models including the outcomes, applications, the possibilities for future work, and improvements of the models. This thesis also includes an appendix to define systematically the physical and physiological properties of lights and photoreceptor systems in the eyes to minimize confusion in the literature between the mathematical and biological models.