Dynamic NREM Sleep Regulation Models

In this chapter we provide an overview about those NREM sleep ­regulation models which take into consideration the effects of external and internal input factors apparently unrelated to the core sleep regulatory mechanisms but deeply influencing their dynamism. McCarley and Massaquoi (J Sleep Res 1(2):132–137, 1992) have begun to incorporate the influence of external noise according to the observations showing frequent brief nonbehavioral EEG and ­polygraphic “awakenings” in sleep. Lo et al. (Proc Natl Acad Sci USA 101(50):17545–1758, 2004) studying brief sleep-wake transitions were able to show that these events can be commonly observed across different species with different sleep patterns. The universality of the distributions of short wake episodes strikingly contrasts the species-specific distributions of sleep bouts. Lo concludes that this relationship reveals a universal regulatory mechanism shaping the dynamism of sleep. Behn et al. (J Neurophysiol 97(6):3828–3840, 2007) created a model of sleep-wake network composed of coupled relaxation oscillation equations. This model could be considered as a crucial one in trying to explain the dual nature of sleep-regulation: gross sleep-wake regulatory mechanisms depending on the already described neural circuitry of the flip-flop switch and fine structure shaped by short bouts of wakefulness. We have hypothesized a parallel regulation of sleep in our model (Halasz et al. J Sleep Res 13(1):1–23, 2004). Tonic processes were hypothesized to involve mainly intracerebral, slow, and chemical influences, while the phasic ones extracerebral, fast, and neuronal-synaptic ones tailoring the interaction of the reciprocal antagonistic influence between the sleep and arousal centers depicted in the flip-flop model of Saper et al. (Trends Neurosci. 24(12):726–731, 2001). The specificity of our model relied in the differential analysis of the descending and ascending slopes of the sleep cycles, which are usually undifferentiated in current models of sleep regulation.