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Deep sleep reinforces the learning of new motor skills

The benefits of a good night’s sleep are now widely known, and now neuroscientists at UC San Francisco have discovered that the animal brain enhances motor skills during deep sleep.

During non-REM sleep, slow brain waves strengthen neural contact points that are directly linked to a newly learned task while awake, while weakening neural links that are not, the researchers found.

“This phenomenon may be related to the notion of ‘getting the gist’ out of how to perform a new task,” said Karunesh Ganguly, MD, PhD, associate professor of neurology. “Sleep appears to reduce neural activity that is unrelated to a task we are learning.”

Better understanding the mechanisms of how sleep affects learning could lead to new medical stimulation devices and consumer-centric wearable devices, or “electroeutics,” that stimulate brain cells and enhance learning for life. nap. Devices from some startups are heading in this direction, but so far they are designed to stimulate the brain while we are awake.

Thought control

Ganguly’s team used a system known as the brain-machine interface (BMI) to better understand how the brain learns new skills during sleep.

The researchers implanted electrodes in the motor region of the rats’ brains to send electrical signals to a computer, which then caused the movement of a detached mechanical device. Because neural circuits are dynamic, the rat brains have rewired themselves to control this device as quickly as it would have if rats practiced new ways of controlling their own limbs.

“People think that BMIs or neuroprosthetics are a way for people with disabilities to walk again or control robotic arms,” said Tanuj Gulati, PhD, postdoctoral researcher and lead author of the new study. “Although this is the ultimate goal, we also use them to understand the learning process in the brain. “

Learn more about sleep

Using such devices, experimenters can create new causal relationships between a neuron and any desired outcome.

“A particular neuron can normally be devoted to controlling a limb, but we can create a new relationship of that neuron with a disembodied external device,” Gulati said.

The redirected neuron, in this case, will quickly help control the external device, and then researchers can track the activity of that neuron to see how the brain integrates this new association.

As noted in an article published in Neuroscience of nature, Gulati and his colleagues connected neurons in rat brains to implanted electrodes, which controlled a mechanical waterspout. The water source was behind a small door opposite the mice.

Because the beak was facing out, the rats had to learn to use a computer-controlled mechanism to move it towards them. As the rats explored several strategies to control the beak, some of which included overt movements, they sometimes activated neurons adjacent to the electrodes. When the right neurons were activated, the computer moved the waterspout.

“Eventually, the rats learn to decouple the actual movements of the beak – they know they don’t really have to pull their arm back or do anything to get it to move,” Gulati said. “All they have to do is voluntarily control the pipe and it will come to them. “

Sleep polishes the wiring

By monitoring the rats ‘brains as they completed this learning process, the team was then able to determine if sleep played a role in making the rats’ freshly made neural connections.

“We saw that after the rats mastered the task while they were awake, some neural models continued to ‘replay’ during sleep,” Gulati said.

These same patterns persisted after the rats woke up, which over time led to improvements in the rats’ performance in the task. Additionally, neural activity that was not needed to gain the waterspout reward had vanished when the rats were retested on the task after they slept.

How Neural Circuits Shape the Brain: 1) Practice Early: Many neurons activate to perform the skill, even those that are not needed.  2) Sleep: The key cells necessary for competence are strengthened.  3) Proficiency mastered: Only vital neurons are triggered.

That sleep is important for basic metabolic maintenance and memory processing is well established, but most of these studies have involved sleep deprivation. While total sleep suppression affects memory, it also causes a number of physiological changes – increases in the stress hormone cortisol, for example, or in anxiety – all of which could contribute to memory degradation.

To get around this complication, the UCSF team used a subtle intervention to reveal sleep’s contribution to successful learning. By using optogenetics – a tool that uses light to turn neurons on or off – scientists were able to suppress neuronal activity in a small region of the brain while the rats were sleeping soundly. Because the optogenetic manipulations are precisely targeted, there was no change in the structure or amount of sleep, only a relatively small adjustment in the triggering patterns of the targeted brain cells.

These experiments showed that the subtle change in neuronal activation during sleep disrupted crucial calculations and eliminated the learning advantage observed previously.

The results confirm that neural patterns truly relevant to the task are examined during sleep, allowing them to survive after sleep to refine motor performance. In particular, this is the first evidence to show that neuronal reactivation and resizing – strengthening and weakening – both occur together during deep sleep.

“This study shows that you can’t ignore sleep,” Gulati said, “whether you are trying to do so in patients trying to regain control of their movements after neural injury or in healthy individuals trying to regain control of their movements after neural injury. learn a new skill. “

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