Unless you’re in your twenties and have a very specific brain chemistry, sleep deprivation is a major bummer. Sleeping poorly — or not sleeping at all — results in physiological and psychological fatigue. This lethargy, in turn, damages the memory-making process. Scientists have known that the hippocampal area of the brain is central to the formation and storage of memories while people sleep. What they didn’t know until now is exactly how this happens.

In a new study published in Nature Communications, scientists report that they’re one step closer to mapping the mysterious intersection between memory formation and sleep. They already knew that, in the hippocampal area, rhythmic and repetitive cycles of electrical activity in the brain occur both spontaneously and in response to certain stimuli. They discovered that these oscillations are controlled by a group of neuron cells called parvalbumin cells, which are located in the hippocampus. They’re also key to preserving memories.

“It seems like this population of neurons that is generating rhythms in the brain during sleep is providing some informational context for reinforcing memories,” senior author and biology professor Sara Aton said in a statement. “The rhythm itself seems to be the most critical part, and possibly why you need to have sleep in order to form these memories.”

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The blue bit is the hippocampus.
The blue bit is the hippocampus.

Aton and her team recorded hippocampal activity in mouse brains to understand the link between its oscillations and memory. They supplied the memories by giving mice a shock on the foot every time they explored the same structure inside a built environment. They then would take the mice back to their cage, let them sleep, and then return them to the structure to get the same shock — a process that eventually created a fear response memory.

But when the conditioned mice were given a drug that inhibited the parvalbumin cells, the mice wouldn’t remember that they were set to receive a shock. The brain patterns of these mice revealed that suppressing these cells would “wipe out the normal learning-associated increase in oscillations in that section of the mouse’s hippocampus.” As the drug prevented the mouse neurons from firing off together and in rhythm, the mice forgot their memory.

The researchers believe that this result likely holds true on the brains of the humans as well — which means that when your brain feels like mush after a bad night’s sleep, it’s because your brain didn’t get the chance to go through the neuron cell driven oscillation patterns it needs to retain memories. This also means that if you’re feeling tired right now, you may want to bookmark this to read again tomorrow.

Photos via Wikimedia Commons, Giphy, Flickr / reynermedia