It is thought the amount of cortisol present can impact the type of memories we are consolidating and potentially the types of dreams we have. Non-REM sleep, where we typically expect fewer dreams, is important for the consolidation of episodic memories (events from your life).Īs our night's sleep progresses, we produce more cortisol - the stress hormone. During REM sleep, our brains consolidate procedural memories (of how to do tasks) and emotions. The brain is "washed" with cerebrospinal fluid, controlled by the glymphatic system.Īt the next level, dream sleep "tidies up" our recent memories and feelings. Deep sleep is when those chemicals are returned to their unused shape. At the molecular level, the chemicals that underpin our thinking are bent out of shape by the day's cognitive activity. In the same way deep sleep helps the body restore its physical capacity, dream sleep " back-flushes" our neural circuits. ![]() REM sleep is important for ensuring our brain is working as it should, as indicated by studies using electoencephalography, which measures brain activity. We tend to have fewer dreams when the weather is hot for the same reason. To protect us, our brain tries to regulate our temperature by "skipping" this sleep stage. Spending less time in REM sleep when we're feverish might happen because we are far less capable of regulating our body temperature in this stage of sleep. We actually experience far less REM sleep when we have a fever - though the dreams we do have tend to be darker in tone and more unusual. Some evidence suggests "fever dreams" are far less common than we might expect. It's like a periscope into a more conscious state, observing what's going on at the surface, then going back down if all is well. The brain activity in REM sleep kicks our brain into gear for a bit. It is typically easier to wake from dreaming if we need to respond to external cues or dangers. Our core body temperature is typically higher while dreaming. Some scientists think we dream in order to stop our brains and bodies from getting too cold. It prevents us from sleeping too deeply and being vulnerable to attack. In humans, REM sleep is thought to occur cyclically every 90 to 120 minutes across the night. But they do not experience the same physiological and behavioural elements that resemble REM dream sleep. ![]() Some jellyfish - who do not have a brain - do experience what could physiologically be characterised as sleep (shown by their posture, quietness, lack of responsiveness and rapid "waking" when prompted). They might even help us imagine what's possible during our waking hours. They wash the thoughts from the day's events at a molecular level. If they're strange or interesting dreams, you might tell someone else about them, which may further encode the dream memory.ĭreams and nightmares are mysterious and we're still learning about them. When dreams or your alarm wake you, you're likely coming out of dream sleep and your dream often lingers into the first few minutes of being awake. That's usually because either really weird thoughts or feelings wake you up or because the last hour of sleep is nearly all REM sleep. While this is not the only time your brain is potentially dreaming - we also dream during other sleep stages - it is the time your brain activity is most likely to be recalled and reported when you're awake. About three or four hours will have been spent in light sleep.įor the remaining time, you were likely in rapid eye movement (REM) sleep. That's because sleep changes with age and exercise affects brain activity. About one or two of these was likely in deep sleep, especially if you're young or physically active. Last night you probably slept for seven to eight hours.
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