Sleep Helps to Form Memories

Sleep can help to form memories, according to an article recently published in Science Magazine. Specifically, deep, slow wave sleep after learning something new will aid in creating the associated new memory.

The study was carried out by scientists at New York University and Beijing University. They used advanced microscopy that allowed them to look inside the living brains of mice. With various experimental conditions, such as having learned a task or not, they were able to observe the formation of new dendritic spines, which are extensions of brain cells that make connections with other brain cells.

The association between sleep and good memory formation has been recognized for a long time. This study, however, showed what was happening at the level of synaptic connections, which has never been demonstrated previously.

The researchers showed that new dendritic spines form on a certain layer of cells in the brain (pyramidal cells). Different learning tasks caused new spines to form on different sets of dendritic branches. Also the new spines were protected from elimination when multiple tasks were learned.

They studied both sleeping animals and ones that were sleep deprived. The sleeping mice had significantly more synaptic connections than those that were not allowed to sleep. They also disrupted sleep at different stages. It is well known that a night’s sleep consists of different stages with some stages producing slow regular brain waves and one stage that is known to occur with rapid eye movements (REM sleep). REM sleep has been associated with dreaming, but REM sleep was not shown to be important in the formation of memories in this study.

The neurons that were activated during motor task learning were reactivated during non-REM sleep. That is, during deep or slow wave sleep. When sleep was disrupted, formation of the dendritic spines and their connections were disrupted. This means sleep contributes specifically to the process of memory storage.

The importance of sleep is being shown again and again by scientists. Sleep has already been shown to be important in the body getting rid of toxins. The body is said to be doing “housekeeping” during sleep and if one does not sleep enough, sluggishness and fatigue are often the result.

Sleep is as important as diet in maintaining health. Just as there is a lot of encouragement to eat right, some say there should be encouragement to sleep right. This is something that corporations might pay attention to when considering the corporate culture and productivity. Long hours at work without enough time for family, play, and sleep may lead to poor productivity, more health problems among employees, and more absenteeism. Recognizing the health benefits of a good night’s sleep will most likely lead to a more energized workforce. The study reported here suggests that one of the benefits to having a proper amount of sleep is sleep helps to form memories. This also must surely affect productivity in the workplace.

This study showed that sleep helps to form memories by strengthening synaptic connections among brain cells. It is still unknown, however, whether sweet memories make for sweet dreams.

By Margaret Lutze

BBC News
Science Vol. 344, Issue 6, Pages 1173-1178

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