Sleep triggers the brain's 'reset switch' to make room for new memory the next day

Researchers have stumbled upon a previously uncharted mechanism of memory in the brain that makes its presence known during sleep.

This “switch” helps clear the proverbial decks, allowing the memory pathways to reset and prepare for a new day of learning. Our brains make it a priority to be able to constantly store new information.

“BARR” phenomenon

The researchers have charmingly dubbed this discovery a “barrage of action potentials” or “BARR.”

In layman’s terms, this implies a burst of neural silence in a specific part of our brain — the hippocampus — enabling the neurons that play a part in memory to rest and regroup for the next round of learning.

It’s like a nightly system reboot that ultimately ensures our brains can keep squirrelling away information without causing a nerve-wracking overload to the neural networks responsible for memory.

Sleeping brain’s role in memory

Oftentimes, the significance of sleep is undermined, but did you know that sleep is vital in maintaining your physical and mental health?

Of course, it recharges your energy batteries, supports your immune function, and helps regulate those sometimes unpredictable emotions. But the aspect we’re particularly interested in is its crucial role in forming memories.

Now, imagine this. When we encounter something new, neurons in our hippocampus go into overdrive as they become active and encode this information.

During our sleep, these dedicated neurons repeat the patterns of activity they observed during the day.

The process, known as memory replay, strengthens the neural connections involved in these experiences, aiding the solidification of the memory.

Unanswered questions about memory and sleep

But as fascinating as it is, a significant question has always been lurking in the background: How does the brain continue learning and storing new information every day without exhausting all available neurons?

If the same neurons are repeatedly used for new memories, wouldn’t they eventually become “full” or overloaded?

In an attempt to address this conundrum, the study set out to investigate how the brain prevents memory circuits from becoming swamped by constant learning.

Azahara Oliva, an assistant professor of neurobiology and behavior at Cornell University, is the lead author of this study.

“We expend about a third of our live sleeping, yet, we don’t know which processes are implemented during this time, in our body but also in our brain, that makes this function so fundamental for our health and in extreme cases, for our survival,” Oliva explained.

Brain structure in forming memories

With the aim of unraveling the mysteries of the hippocampus and its role in memory storage during sleep, the research team turned to mice.

Given their similar brain structure to humans, especially concerning the hippocampus, mice make the perfect subjects for memory-related studies.

Using a mix of advanced techniques, including electrode implants and optogenetics, the research team was able to monitor and manipulate neuronal activity in the hippocampus.

Electrodes provided the much-needed insight into specific brain regions, while optogenetics gave the ability to control genetically modified neurons with light.

A key feature of the experiment was observing and recording sharp-wave ripples or SWRs. These are brief bursts of brain activity that occur in the hippocampus during deep sleep and are thought to be crucial for replaying memories and strengthening neural connections.

However, during these observations, the research team noticed something new – a previously unobserved brain event during sleep: the BARR.

Finding the BARR “reset switch”

Dubbed the “reset button” for neurons in the hippocampus, the BARR event is significant. It occurs during sleep when the brain is replaying memories through SWRs, and certain neurons in the CA2 region switch off.

This period of silence allows the neurons that were heavily used during learning to reset, preparing them for new learning the next day.

“We were very surprised to find that this phenomenon of memory resetting is an active process: if we block memory resetting by silencing the neurons responsible for it, the memory doesn’t get consolidated properly,” Oliva said.

“This means that memory is a two-fold process, with neural circuits that enhance the consolidation of a given experience and neural circuits that control that this consolidation doesn’t go over a healthy limit.”

Sleep, memory, and future research

Though this study has shed some light on how the brain manages memory during sleep, it leaves quite a few questions unanswered.

One limitation is that the study was conducted in mice, with brain structures similar to humans but not identical.

Further research will be needed to confirm whether these findings apply directly to human memory consolidation.

The researchers now plan to investigate several key questions:

• How does the brain know which neurons are to be consolidated and reset?
• What is the marker?
• How much can memory be boosted without saturating the brain?
• And is it possible to use the reset mechanisms to erase unwanted memories?

“We don’t know this yet,” Oliva explained.

So, the next time you lay your head down for a good night’s sleep, remember that it’s not just your body that’s resting. Your brain is diligently consolidating memories, replaying the day’s events, and hitting that essential reset button to ensure it’s ready for the new day’s learning.

The study is published in the journal Science.

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