The Reason Why We Need Sleep

We sleep to rest and regain our strength, and the benefits of a good night's sleep seems obvious, but what is it about sleep that improves our brain performance, at the cellular levels, that's an old debate to which a new study tried to put an end.

The opinions are divided into two camps: one believes that sleep reduces the unimportant connections between neurons, thus preventing brain overload, while the other insists that sleep consolidates memories from the previous day.

So a group of researchers led by Lior Appelbaum and Philippe Mourrain of Stanford University, thought that studying the larvae of the zebrafish, a common see-through aquarium pet, would settle this once and for all.

Zebrafish, just like humans, are active during the day and sleep during the night, but luckily for us humans, these fish are transparent, so for this research, scientists could see their brains as they slept.

The larvae neurons were tagged with a dye, so that the synapses – the active neurons connections, appear green and the inactive connections appear black.

After following the zebrafish for a day, the researchers concluded that during sleep, their synaptic activity decreased, shutting down all the unnecessary memory connections, and that this pattern was different from memory consolidation.

“Sleep is an active process that reduces the activity in the brain,” said Mourrain.

“It allows the brain to recover from past experiences.”

He explains that without the synapse reduction that happens during sleep, the brain would not be able to continually assimilate and store new information.

But the debate is not settled yet, since it seems that the team also found that not all neural circuits are affected by sleep in the same way, and Mourrain says that in this case, learning and memory may benefit the most.

So as neuroscientist Jan Born of the University of Lübeck in Germany said, the two hypotheses about sleep “may not be mutually exclusive”.

A resolution should be found soon, since Mourrain and Applebaum’s new imaging technique will allow more detailed study of the brain during sleep, in years to come.

The results of the first study to show the effects of sleep/wake cycles and time of day on the synapses of a living vertebrate, were published in the journal Neuron.