Remembering what you learn appears to be tied to the body's circadian rhythm, a new study suggests. Researchers found that animals whose internal clock was manipulated lost their short-term memory. Interfering with the sleep, wake cycle increase the amount of a chemical in the brain that keeps the brain active. This overwhelmed the part of the brain responsible for memory. Researchers say this "overwhelmed" state is also found in people with Down's Syndrome, and people with Alzheimer's disease.