Lack of sleep may cause the brain to stop producing new cells. A study on rats showed that lack of sleep caused a stress hormone to affect the hippocampus, a brain region involved in forming memories.
Rats who were deprived of sleep for 72 hours had higher levels of the stress hormone corticosterone, and as a result produced significantly fewer new brain cells in a region of the hippocampus.
When corticosterone levels were kept at a constant level, the hippocampus produced a normal amount of new cells. After the animals were restored to normal sleep patterns, it took two weeks for nerve cell production levels to normalize.