Brain Replays Memories And Stores The Highlights While We Sleep

Jim Carrey has memories of a painful relationship wiped from his brain in Eternal Sunshine of the Spotless Mind 

We may think we are asleep – but deep in the recesses of our mind a “memory editor” is working overtime, replaying the experiences of the day and storing the highlights on our brain’s version of a video recorder, claim scientists.
Researchers have discovered that the mind keeps most memories for just a day but then at night acts like a film editor sifting through the “video clips” before transferring the best bits to long term storage in our own movie archive.

The research has “profound implications” for the importance of sleep and its link with long term memory, they said.

It could also one day lead to ways of influencing the brain in deciding what are healthy and unhealthy memories to keep, such as in the film Eternal Sunshine of the Spotless Mind.

“Ours is the first study to demonstrate this link between memory replay and memory consolidation,” claims Professor Susuma Tonegawa at the Picower Institute for Learning and Memory, an offshoot of the American university MIT.

“The sleeping brain must replay experiences like video clips before they are transformed from short-term into long-term memories.”

Scientists have long suspected that there is a link between sleep and memory and have suggested that it acts like a sort of filing system, enabling the brain to distinguish between important and useless information.

Dreams – which usually occur in light sleep known as Rapid Eye Movement – are thought to be part of the process.

But in memory tests Prof Tonegawa discovered that it was more likely that deep sleep – technically known as slow wave sleep – which played a role.

Prof Tonegawa and his team used experiments in humans and mice to show that memories are first stored in the hippocampus, a sea horse shaped part of the central brain, before being “replayed” and then being filed in the outer neocortex, otherwise known as grey matter.

He discovered the link in experiments where volunteers were asked to memorise sets of words and then half of them were allowed to go to sleep immediately afterwards and half were kept awake.

He discovered that those who slept greatly increased their ability to recall the words up to six weeks later.

Then with experiments in mice he was able to establish which parts of the brain were involved in the process. Using censors in the brain he discovered that the hippocampus and the neocortex remained very active at night and that it appeared that the information was transferred between the two along a circuit known as the “trisynaptic pathway”.

Creating a strain of genetically engineered mice in which a change of diet shuts down trisynaptic pathway, scientist followed their brain activity as they found their way around a maze.

While they were still awake and running, neurons in the mice fired in a certain sequence which was then repeated during slow wave sleep suggesting it was “replaying” the memory.

By blocking the trisynaptic pathway, scientists found they were also able to block the formation of long term memories.

The animals were able to form long-term memories of the maze only when their trisynaptic pathways were functioning after the formation of the short-term memory.

They concluded that the pathway played a “crucial role” in transferring from short to long term memory storage.

In the film Eternal Sunshine of the Spotless Mind, a couple undergo a procedure to erase each other from their memories when their relationship turns sour.

Via Telegraph