We lose our ability to make sound decisions because we can no longer accurately assess the situation, plan accordingly, and choose the correct behavior. Being chronically tired to the point of fatigue or exhaustion means that we are less likely to perform well.

Studies of the connection between sleep and declarative memory have had mixed results, and this is an area of continued research.

Research has also focused on sleep and its role in procedural memory—the remembering "how" to do something (for example, riding a bicycle or playing the piano).

Although chronic sleep deprivation affects different individuals in a variety of ways (and the effects are not entirely known), it is clear that a good night’s rest has a strong impact on learning and memory.

Although current research suggests that sleep is essential for proper memory function, there are unanswered questions, as in any area of active scientific inquiry.

Lapses in focus from sleep deprivation can even result in accidents or injury.

For more information about how sleep deprivation affects performance, see Sleep, Performance, and Public Safety.

Low-quality sleep and sleep deprivation also negatively impact mood, which has consequences for learning.

Alterations in mood affect our ability to acquire new information and subsequently to remember that information.

Further studies have suggested that REM sleep seems to be involved in declarative memory processes if the information is complex and emotionally charged, but probably not if the information is simple and emotionally neutral.