Measuring sleep-wake rhythms
Whereas traditional outcome measures in circadian rhythm research tend to be limited to descriptions of amplitude and phase, we have proposed, developed and successfully applied two new parameters, one quantifying the stability of a behavioral or physiological 24-hour profile over multiple days, the other quantifying the fragmentation of behavioral or physiological states over multiple short periods rather the typical 24-hour periodicity. We showed that these parameters are more sensitive measures for sleep-wake rhythm disturbances than traditional sleep or circadian measures in studies on human aging (Huang et al., 2002), Alzheimer’s disease (Hatfield et al., 2004) and adult ADHD (Boonstra et al., 2007), as well as in a primate model for accelerated aging (Cayetanot et al., 2005). Moreover, the parameters are strongly related to cognitive abilities in aging (Oosterman et al., 2008) and dementia (Carvalho-Bos et al., 2007) and even better predictors of age-related atrophy of the medial temporal lobe than age per se is (Van Someren et al., 2008). Optimization of assessment of rhythms in activity and melatonin has been described in two papers (Van Someren, 2007; Van Someren and Nagtegaal, 2007) and a theoretical review (Van Someren and Riemersma – Van Der Lek, 2007) puts forward a model on the mechanisms involved in the disruptive effects on rhythm fragmentation on central and peripheral circadian oscillators, brain function and health.