What Do Our Brains Actually Do While We Sleep?

What Do Our Brains Actually Do While We Sleep?
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Why do we dream during sleep? originally appeared on Quora - the place to gain and share knowledge, empowering people to learn from others and better understand the world.

Answer by Mariano Sigman, Founder of the Integrative Neuroscience Laboratory of the University of Buenos Aires, on Quora:

The brain does not shut off at night. In fact, while we sleep, neurons engage in sustained activity which sets up in motion key facets of the cognitive apparatus. For example, during one of the first phases of sleep – slow wave – memory is consolidated. So after a few hours of sleep or even a quick nap, we remember better what we’ve learned over the course of the day

By taking a closer look through experiments on the cellular and molecular level, we now know that this process involves rhythmic waves of activity which connect neurons in the hippocampus and the cerebral cortex. These cycles of neuronal activity replay patterns that were engaged during the day, which may be seen as a contemporary physiological version of one of Freud’s main ideas about sleep, the remains of the day. Actually, by reinforcing this mechanism (simply by playing tones at the same frequency of this brain rhythms) memory can be further improved, and sleepers learn more than they would solely by passive sleep.

While slow wave sleep is a state in which waking neuronal activity is repeated, during REM sleep (when we dream) more variable neuronal patterns are generated, with the ability to recombine pre-existing patterns of neural activity. This has lead my friend and colleague Sidarta Ribeiro to suggest two roles for dreaming:

The first is that REM sleep is a state conducive to creating new ideas and connecting elements of thought that were disconnected during the day, and so dreams are a creative thought factory. This goes well in line with many stories of people struggling for days with ideas and finding the solution in a dream. One of the most spectacular cases was Paul McCartney, who woke up in his bedroom on Wimpole Street with the melody to ‘Yesterday’ in his head.

The second ones is that dreams enhance one of the most fabulous human virtues: our capacity to simulate the future and foresee the consequences of our own actions. To release from the immediacy of the present asking questions like: How would it be if? What might happen if…?

Indeed dreams (like play) are a fertile ground for mental simulation in which the body is not exposed (we can die in a dream, or in a game, and we learned something while life still goes on…). In fact, this disconnection between the mind and the body is literal; when we dream there is an inhibition of the motor neurons through which the brain controls and governs the muscles, generating a brain chemistry that is very distinct from our waking one.

Sidarta has some experiments showing that during dreams, rodents engage in neural patterns of activity of task they will engage in the next days as if they would be simulating the future and anticipating it in dreams. This may explain why for many years and throughout cultures, dreams have been perceived as oracles. There is no magic or esoteric thinking to reach to this conclusion, it is maybe after one of the reasons why we dream.

Long live the dreams! Our societies recognize the merits of our own and others’ lives through the achievements we make while awake but there is no merit in being a good dreamer. As in Jorge Luis Borges story “The circular ruins” maybe we should pay more attention and be more concerned about forging good dreams.

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