Local Aspects of Avian Non-REM and REM Sleep

Abstract

Birds exhibit two types of sleep that are in many respects similar to mammalian rapid eye movement (REM) and non-REM (NREM) sleep. As in mammals, several aspects of avian sleep can occur in a local manner within the brain. Electrophysiological evidence of NREM sleep occurring more deeply in one hemisphere, or only in one hemisphere – the latter being a phenomenon most pronounced in dolphins – was actually first described in birds. Such asymmetric or unihemispheric NREM sleep occurs with one eye open, enabling birds to visually monitor their environment for predators. Frigatebirds primarily engage in this form of sleep in flight, perhaps to avoid collisions with other birds. In addition to interhemispheric differences in NREM sleep intensity, the intensity of NREM sleep is homeostatically regulated in a local, use-depended manner within each hemisphere. Furthermore, the intensity and temporo-spatial distribution of NREM sleep-related slow waves varies across layers of the avian hyperpallium – a primary visual area – with the slow waves occurring first in, and propagating through and outward from, thalamic input layers. Slow waves also have the greatest amplitude in these layers. Although most research has focused on NREM sleep, there are also local aspects to avian REM sleep. REM sleep-related reductions in skeletal muscle tone appear largely restricted to muscles involved in maintaining head posture. Other local aspects of sleep manifest as a mixture of features of NREM and REM sleep occurring simultaneously in different parts of the neuroaxis. Like monotreme mammals, ostriches often exhibit brainstem-mediated features of REM sleep (muscle atonia and REMs) while the hyperpallium shows EEG slow waves typical of NREM sleep. Finally, although mice show slow waves in thalamic input layers of primary sensory cortices during REM sleep, this is not the case in the hyperpallium of pigeons, suggesting that this phenomenon is not a universal feature of REM sleep. Collectively, the local aspects of sleep described in birds and mammals reveal that wakefulness, NREM sleep, and REM sleep are not always discrete states.

Does the Mind Wander When the Brain Takes a Break? Local Sleep in Wakefulness, Attentional Lapses and Mind-Wandering

“…Within NREM sleep, some brain regions can show slow waves while others do not (Nir et al, 2011; Nobili et al, 2011). Such regional aspects of sleep activity had already been observed in certain animal species (e.g., dolphins who can enter unihemispheric sleep, sleeping in one brain hemisphere at a time) (Mascetti, 2016; Rattenborg et al, 2019) and in sleep pathologies (Terzaghi et al, 2009; Dodet et al, 2015; Castelnovo et al, 2016; Riedner et al, 2016). However, in the past few years, local sleep involving changes in sleep depth within NREM sleep has been robustly observed in individuals without sleep disorders (Huber et al, 2004; Nir et al, 2011).…”

Does the mind wander when the brain takes a break? Local sleep in wakefulness, attentional lapses and mind-wandering

“…Such regional aspects of sleep activity had already been observed in certain animal species (e.g. dolphins who can enter unihemispheric sleep, sleeping in one brain hemisphere at a time) (Mascetti, Gian Gastone, 2016;Rattenborg et al, 2019) and in sleep pathologies (Castelnovo et al, 2016;Dodet et al, 2015;Riedner et al, 2016;Terzaghi et al, 2009). However, in the past few years, local sleep involving changes in sleep depth within NREM sleep has been robustly observed in individuals without sleep disorders (Huber et al, 2004;Nir et al, 2011).…”

A Paradoxical Kind of Sleep in Drosophila melanogaster

“…4 Because most sleep is evidenced by behavioral quiescence, this criterion alone is probably insufficient to discriminate between distinct forms of sleep and consequently between potentially different sleep functions. Although it has long been accepted that distinct sleep stages, such as slow-wave sleep (SWS) and rapid eye movement (REM) sleep, exist in mammals and birds, [5][6][7] only recently has the possibility of sleep stages been explored in other animals, such as reptiles, 8 fish, 9 and invertebrates, such as cuttlefish. 10 To be able to properly understand sleep biology requires disambiguating various forms of sleep, as these may be accomplishing different functions that could be confused if grouped together simply under behavioral quiescence alone.…”