Scientists find neurons that purge our minds of unnecessary memories while in REM sleep

We forget most of our dreams when we wake thanks to a group of neurons that work while we sleep to purge our minds of unnecessary memories, scientists found. The neurons -- which carry messages from cells that make a hormone involved in both sleep and appetite -- are active in the REM phase of sleep in which we dream. The finding adds to previous research that showed that sleep is the time that we store memories from the day for the long-term. Researchers studied the neurons and hormone-making cells in mice, which they found to be more forgetful when the cells were artificially activated. REM -- or'rapid eye movement' -- sleep is one of the several sleep cycles the body goes through each night.