Sleep has been detected in every animal that has been adequately studied (Cirelli & Tononi, 2008). The ubiquitous nature of sleep suggests that it evolved early in the course of evolution and therefore may serve a conserved function essential to all animals. This hypothesis forms the rationale behind the development of “simple” animal models of sleep (Allada & Siegel, 2008; Mignot, 2008). By studying sleep in animals such as the fruit ﬂy (Drosophila melanogaster), where the power of genetic techniques can be readily employed,we may gain insight into the initial (perhaps cellular) function of sleep, a function that may still be relevant to understanding sleep in humans. Indeed, recent studies have already demonstrated remarkable similarities between sleep in Drosophila and sleep in mammals (Hendricks, Finn, Panckeri, et al., 2000; Shaw, Cirelli, Greenspan, et al., 2000; reviewed in Cirelli & Bushey, 2008). Although the utility of studying sleep in“simple”animal models is undeniable, it is unlikely that this approach alone will tell the whole story, especially given that Drosophilado not exhibit brain states comparable to mammalian slow-wave sleep (SWS) and rapid eye-movement (REM) sleep (Cirelli, 2006; Cirelli & Bushey, 2008; Hendricks & Sehgal, 2004; Nitz, van Swinderen, Tononi, et al., 2002). Indeed, the heterogeneous nature of mammalian sleep suggests that the speciﬁc changes in brain activity that accompany SWS and REM sleep might serve secondarily evolved functions not found in simple animals. Interestingly, birds, as the only non-mammalian taxonomic group to exhibit unequivocal SWS and REM sleep (Klein, Michel, & Jouvet, 1964; Ookawa & Gotoh, 1964;reviewed in Amlaner & Ball, 1994), provide a largely unrecognized opportunity to glean insight into the functions of these states by revealing overriding principles common to both lineages (Rattenborg, Martinez-Gonzalez, Lesku, et al., 2008a).
This chapter summarizes our current understanding of avian sleep. We ﬁrst describe the basic changes in brain activity and physiology that accompany avian SWS and REM sleep. Although we emphasize the similarities between avian and mammalian sleep, potentially meaningful differences are also discussed. Finally, we summarize our recent proposal that the convergent evolution of similar sleep states in mammals and birds is linked to the convergent evolution of relatively large and highly interconnected brains capable of complex cognition in each group (Rattenborg, 2006a; Rattenborg, Martinez-Gonzalez, & Lesku, 2009).
- evolution of sleep,
- sleep physiology
Available at: http://works.bepress.com/charles_amlaner/9/