Sleeping serves many different functions. One of these is to help us remember experiences we had during the day. REM sleep is thought to be?important for emotional memories?(for example, memories involving fear) or?procedural memory?(such as how to ride a bike). On the other hand, slow-wave sleep is thought to reflect the storing of so-called??declarative? memories?that are the conscious record of your experiences and what you know (for example, what you had for breakfast).
We also know experiences are??replayed? in the brain while we are sleeping – the memories of these experiences are like segments from a movie that can be rewound and played forward again. Replay occurs in neurons in the hippocampus -?a brain region important for memory?- and has been best studied in rats learning to navigate a maze. After a navigation exercise, when the rat is resting, its brain replays the path it took through the maze. Replay helps to?strengthen the connections between brain cells, and is therefore thought to be important for consolidating memories.
But is it that important for you to remember what you had for breakfast? Probably not ? that?s why the brain needs to be selective about what it remembers. Sleeping allows the brain to sift through memories, forgetting certain things so as to remember what?s important. One way it may do this is by ?pruning away? or ?scaling down? unwanted connections in the brain.
A leading theory of sleep function – the ?synaptic homeostasis hypothesis? – suggests that during sleep there is a widespread?weakening of connections?(known as ?synapses?) throughout the brain.
This is thought to counterbalance the overall strengthening of connections that occurs during learning when we are awake. By pruning away excess connections, sleeping effectively ?cleans the slate? so we can learn again the next day.?Interfering with this scaling down process?can, in some cases, lead to more intense (and perhaps unwanted) memories.
The importance of sleep for keeping our brains optimally active may be reflected in how our sleeping patterns change as we age.?Babies and children sleep much more than adults, probably because their developing brains are learning much more, and being exposed to new situations.
Later in life,?sleep declines and becomes more fragmented. This may reflect either a reduced need for sleep (as we are learning less) or a breakdown in sleep processes as we age.?Overall, the evidence suggests having healthy sleep patterns is key to having a healthy and well-functioning brain.