Longer rest bouts are more common at night. D, Rest bout distribution (average number of times each rest bout occurred per fly ± SEM for day and night). * p < 0.05 by t test comparison of means. Right: Average rest bout length (± SEM) for the same flie. ** p < 0.01 by t test comparison of means. C, Left: Average minutes rest per hour (± SEM) for tethered female flies on an air-suspended ball (prepared for electrophysiology), for day (white) and night (black). Threshold for inactivity is indicated by the red line. Bottom: Activity pattern for a sample fly during the day (white bar) and night (black bar). Top: A pixel subtraction method defines fly movement. B, Fly movement is quantified from a filmed experiment. Recording brain activity in behaving flies. Our results show that sleep is not homogenous in insects, and suggest that waking behavior and the associated synaptic plasticity mechanisms determine the timing and intensity of deep sleep stages in Drosophila. Optogenetic upregulation of cyclic adenosine monophosphate during the day increases sleep intensity at night, whereas loss of function of a molecule involved in synaptic pruning, the fragile-X mental retardation protein, increases sleep intensity during the day. Two molecules linked to synaptic plasticity regulate the intensity of the first deep sleep stage. As in mammals, the timing and intensity of these dynamic sleep processes in flies is homeostatically regulated and modulated by behavioral experience. Here we used electrophysiology and arousal-testing paradigms to show that the fruit fly, Drosophila melanogaster, transitions between deeper and lighter sleep within extended bouts of inactivity, with deeper sleep intensities after ∼15 and ∼30 min of inactivity. Evidence for different sleep stages in invertebrates remains elusive, even though it has been well established that many invertebrate species require sleep (Campbell and Tobler, 1984 Hendricks et al., 2000 Shaw et al., 2000 Sauer et al., 2003). You can breathe, and your heart is working, but you really can’t move.How might one determine whether simple animals such as flies sleep in stages? Sleep in mammals is a dynamic process involving different stages of sleep intensity, and these are typically associated with measurable changes in brain activity (Blake and Gerard, 1937 Rechtschaffen and Kales, 1968 Webb and Agnew, 1971). Do you ever feel like you can’t escape during a dream? Well, the truth is, you can’t. Voluntary muscles become paralyzed, and this period of paralysis is a built-in protective measure to keep you from harming yourself. REM sleep is when you typically dream because of increased brain activity. Your brain and other body systems become more active while your muscles become more relaxed. REM sleep is characterized by eye movement, increased respiration rate and increased brain activity. Most dreaming occurs during Stage 5, known as REM. If aroused from sleep during these stages, a person may feel disoriented for a few minutes. These stages are known as slow-wave, or delta, sleep. These are deep sleep stages, with Stage 4 being more intense than Stage 3. At this point, the body prepares to enter deep sleep.

Stage 2:ĭuring this light period of sleep the heart rate slows and the body temperature decreases. During this time, you may feel like youʼre falling, which may cause you to jump suddenly (called hypnic myoclonia). The eyes are closed during Stage 1 sleep and you can be awakened without difficulty however, if aroused from this stage of sleep, you may feel as if you havenʼt slept.

Deep sleep stage