Defining and determining the properties of the human sleep homeostat

To summarize, the principal findings upon which this thesis is built, are these: 1. The most accurate measure of the human chronotype on the 24-h scale relative to external time is the timepoint at a point in the 30–40% range of habitual sleep length on free days. 2. The free-day mid-sleep time correlates negatively with the gain constant from Achermann’s elaboration of the two-process model. Age is a confounding factor in this relationship, which itself is positively associated with the gain constant. 3. The gain constant describes the gradual dissipation of Process S while allowing for the inherently irregular course of SWA. 4. A new parameter (Process Z) is introduced to describe the local cortical differentiation of the kinetics of SWA homeostasis as distinct from the more global, integrative Process S involved in the timing of sleep onset and end. 5. Rather than conventional delta range (0.75–4.5Hz), 2–3Hz is the frequency range in which SWA homeostasis is clearest. 6. Frontal, use-dependent cortical areas are involved in SWA regulation the most, while occipital SWA exhibits slightly different characteristics. SWA response may not be immediate to current demand in these areas.