Written by Lila Cart; Illustration by Monica Oh

In 2008, researchers found that adult wild sloths sleep around 10 hours a day. This is much less than the 16 hours found from the previous research done in 1983 with captive sloths. This discrepancy may in part be due to a mix of adults and juveniles in the previous study or differences in the capacity to sleep between captive and wild animals.

Wakefulness and sleep can be measured using an electroencephalogram (EEG) and an electromyogram (EMG). Different patterns of electrical activity distinguish each state. Sleep can be split into two phases. The first phase of sleep is slow wave (sometimes called non-REM), where the brain relaxes its metabolism and recovers from its awake activity. This phase can be further split into stages 1-4. Stage 1 is the lightest stage with stage 4 is the deepest. The second phase of sleep is REM, Rapid Eye Movement. During this phase, the body is paralyzed and dreaming occurs. Dreams often incorporates and recombine fragments of our recent waking memories. Scientists are still working to understand the function of REM sleep and dreaming.

There are many regulators of sleep and wakefulness, ranging from chemical messengers to environmental stimuli. While many regulators feed into the system, sleep is controlled with a unique type of circuit. Its an example of a flip-flop circuit, meaning that when one part of the circuit is on the other is shut off. This is unlike many regulatory systems which involve creating a balance of positive and negative messengers. Once sleep is turned on, REM sleep is also controlled by a flip-flop circuit.