Study links sleep to memory storage of newly learned materials

A study from the University of Michigan suggests that groups of neurons activated during prior learning maintain curves and build memories to your brain during sleep.

UM researchers have been studying how memories related to a specific sensory event are created and stored in mice. In a study conducted before the coronavirus pandemic and recently published in Nature Communications, the researchers examined how intimidating memory was created in relation to specific visual stimuli.

They found that not only did the neurons activated by the visual stimulus remain more active during subsequent sleep, but sleep is also critical for their ability to link the fear memory to the sensory event. .

Previous research has shown that areas of the brain that are highly active during intense learning tend to show more activity during subsequent sleep. But what was not clear was whether this “revival” of bedtime memories was needed to store a memory full of newly learned materials.

“Part of what we wanted to understand was whether there is communication between parts of the brain that centralize fear memory and the specific neurons that centralize sensory memory to which fear is associated. How do they talk together, and have to do so during sleep? We want to find out what enables that process of forming a new association, as a specific set of neurons, or a certain level of sleep, “said Sara Aton, senior study author and professor in the UM Department of Molecular, Cellular and Developmental Biology. “But for the longest time, there was really no way to test this.”

Now, researchers have the tools to tag cells that are expertly activated during a particular window. Focusing on a specific set of neurons in the primary visual cortex, Aton and the study’s lead author, graduate student Brittany Clawson, created a visual memory test. They showed a neutral image to a group of mice, and expressed genes in the visual cortex neurons that activated the image.

To confirm that these neurons recorded the neutral image, Aton and her team tested whether they were able to trigger the image’s stimulus memory by selectively activating the neurons without showing them the image. . When they activated the neurons and activated them with a gentle foot shock, they found that their subjects were frightened by visual stimuli that looked similar to the image these cells emit. coding. They also found the opposite to be true: after repairing the visual stimulus with a foot shock, their subjects would respond with a fear of reactivation of the neurons.

“Basically, the precept of the visual stimulus and the principle of this completely artificial activation of the neurons created the same response,” Aton said.

The researchers found that when disturbed sleep after showing the subjects an image and giving them a gentle foot shock, there was no fear associated with the visual stimulus. Those with uncontrolled sleep learned to fear the specific visual stimulus paired by foot shock.

“We found that these mice were intimidated by every visual stimulus we showed them,” Aton said.

“From the moment they go to the room where the visual stimuli are given, they seem to know that there is a reason to feel fear, but they do not know what specifically fear is. orra. “

This tends to show that, in order to be able to properly link fear with visual stimuli, they must have a sleep-related reaction of the neurons encoding that stimulus in the sensory cortex, according to Aton. This allows a memory unique to that scene to be created. The researchers believe, at the same time, that sensory cortical area needs to communicate with other brain structures, in order to marry the sensory side of memory to the emotional side.

Aton says their findings may have an impact on the understanding of post-traumatic stress anxiety and disorder.

“To me this is a kind of idea that says, if you associate fear with a certain specific event during sleep, a sleep disturbance can affect this process. Without sleep, the brain appears to be manages to manipulate the fact that you are afraid, but you may not be able to relate that to the things that you should be afraid of, “Aton said.

“That assignment process may be one that goes awry with PTSD or generalized anxiety.”

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