February 26, 2024

Why Do Humans Sleep? Scientists Find Clues for Solving This Age-Old Mystery

Why do humans sleep? According to the lead author of the research and neurologist Daniel Rubin, MD, Ph.D., of the MGH Center for Neurotechnology and Neurorecovery, scientists have long understood that during sleep, a phenomenon known as “replay” takes place.” This is the most direct evidence of replay from the motor cortex thats ever been seen during sleep in humans,” states Rubin. Most of the replay identified in the study occurred throughout slow-wave sleep, a stage of deep rest. Surprisingly, replay was much less most likely to be spotted while T11 was in REM sleep, the stage most commonly associated with dreaming.

According to the scientists, this research study discovered the clearest indication of motor cortex replay throughout human sleep that has actually ever been seen.
When sleeping might assist in the development of tools for those suffering from neurologic illness or damage, New insights into brain activity
Why do humans sleep? This concern has actually been discussed by researchers for hundreds of years, but a current research study from Massachusetts General Hospital (MGH) scientists that was brought out in partnership with professionals from Brown University, the Department of Veterans Affairs, and a number of other organizations adds new hints for fixing this mystery.
According to the lead author of the research study and neurologist Daniel Rubin, MD, Ph.D., of the MGH Center for Neurotechnology and Neurorecovery, researchers have long understood that throughout sleep, a phenomenon called “replay” takes place. Replay is thought to be a mechanism utilized by the brain to remember new information. When a mouse is taught to navigate a labyrinth, keeping track of devices might suggest that an exact pattern of brain cells, or neurons, illuminate as it follows the correct course. “Then, later, while the animal is sleeping, you can see that those nerve cells will fire again because exact same order,” states Rubin. Researchers theorize that this is how the brain practices freshly acquired knowledge during sleep, allowing memories to be combined– that is, turned from short-term memories to long-lasting memories.
Replay, however, has only been appropriately shown in lab animals. “Theres been an open concern in the neuroscience neighborhood: To what extent is this model for how we discover things real in people? And is it true for different kinds of learning?” asks neurologist Sydney S. Cash, MD, Ph.D., co-director of the Center for Neurotechnology and Neurorecovery at MGH and co-senior author of the research study. Importantly, says Cash, comprehending whether replay accompanies the learning of motor skills could assist guide the advancement of brand-new therapies and tools for individuals with neurologic illness and injuries.

Scientists have actually discovered the very first proof of replay in the human motor cortex, which manages voluntary movement, in a new research study. This may offer insights to the designers of assistive tools for individuals with paralysis and also offer information about how we discover and develop long-lasting memories. Credit: Massachusetts General Hospital
To study whether replay takes place in the human motor cortex– the brain area that governs movement– Rubin, Cash, and their associates got a 36-year-old male with tetraplegia (likewise called quadriplegia), indicating he is not able to move his upper and lower limbs, in his case due to a spine cord injury. The guy, identified in the research study as T11, is a participant in a clinical trial of a brain-computer user interface device that permits him to utilize a computer cursor and keyboard on a screen.
In the study, T11 was asked to perform a memory task comparable to the video game Simon, in which a player observes a pattern of flashing colored lights, then needs to recall and recreate that sequence. He controlled the cursor on the computer screen just by considering the motion of his own hand. Sensors implanted in T11s motor cortex measured patterns of neuronal firing, which showed his intended hand motion, allowing him to move the cursor around on the screen and click it at his desired places. These brain signals were tape-recorded and wirelessly transferred to a computer.
That night, while T11 slept at house, activity in his motor cortex was recorded and wirelessly transferred to a computer. “What we discovered was pretty incredible,” says Rubin. “He was basically playing the video game overnight in his sleep.” On several occasions, states Rubin, T11s patterns of neuronal firing throughout sleep exactly matched patterns that occurred while he performed the memory-matching game previously that day.
” This is the most direct evidence of replay from the motor cortex thats ever been seen throughout sleep in people,” says Rubin. Many of the replay spotted in the research study happened throughout slow-wave sleep, a phase of deep rest. Interestingly, replay was much less most likely to be detected while T11 was in REM sleep, the stage most typically associated with dreaming. Rubin and Cash see this work as a structure for finding out more about replay and its function in knowing and memory in people.
” Our hope is that we can take advantage of this details to help build much better brain-computer interfaces and develop paradigms that help people discover more quickly and efficiently in order to regain control after an injury,” says Cash, noting the significance of moving this line of questions from animals to human topics. “This kind of research advantages immensely from the close interaction we have with our participants,” he adds, with thankfulness to T11 and other individuals in the BrainGate scientific trial.
Hochberg concurs. “Our unbelievable BrainGate participants offer not just useful feedback toward the development of a system to bring back communication and movement, but they likewise offer us the unusual chance to advance fundamental human neuroscience– to understand how the human brain works at the level of circuits of specific nerve cells,” he states, “and to utilize that details to build next-generation restorative neurotechnologies.”
Rubin is likewise an instructor in neurology at Harvard Medical School (HMS). Money is an associate teacher of Neurology at HMS. Hochberg is a senior speaker on Neurology at HMS and a professor of Engineering at Brown University.
The study was moneyed by the National Institute of Neurologic Disease and Stroke, the American Academy of Neurology, the National Institute of Mental Health, Conquer Paralysis Now, the Department of Veterans Affairs, the MGH-Deane Institute, and the Howard Hughes Medical Institute at Stanford University.
Reference: “Learned Motor Patterns Are Replayed in Human Motor Cortex during Sleep” by Daniel B. Rubin, Tommy Hosman, Jessica N. Kelemen, Anastasia Kapitonava, Francis R. Willett, Brian F. Coughlin, Eric Halgren, Eyal Y. Kimchi, Ziv M. Williams, John D. Simeral, Leigh R. Hochberg and Sydney S. Cash, 22 June 2022, Journal of Neuroscience.DOI: 10.1523/ JNEUROSCI.2074-21.2022.