![]() ![]() Interestingly, replay was much less likely to be detected while T11 was in REM sleep, the phase most commonly associated with dreaming. Most of the replay detected in the study occurred during slow-wave sleep, a phase of deep slumber. “This is the most direct evidence of replay from motor cortex that’s ever been seen during sleep in humans,” says Rubin. “He was basically playing the game overnight in his sleep.” On several occasions, says Rubin, T11’s patterns of neuronal firing during sleep exactly matched patterns that occurred while he performed the memory-matching game earlier that day. “What we found was pretty incredible,” says Rubin. ![]() That night, while T11 slept at home, activity in his motor cortex was recorded and wirelessly transmitted to a computer. These brain signals were recorded and wirelessly transmitted to a computer. Sensors implanted in T11’s motor cortex measured patterns of neuronal firing, which reflected his intended hand movement, allowing him to move the cursor around on the screen and click it at his desired locations. He controlled the cursor on the computer screen simply by thinking about the movement of his own hand. ![]() In the study, T11 was asked to perform a memory task similar to the electronic game Simon, in which a player observes a pattern of flashing colored lights, then has to recall and reproduce that sequence. Hochberg of MGH, Brown University, and the Department of Veterans Affairs. The investigational device is being developed by the BrainGate consortium, a collaborative effort involving clinicians, neuroscientists, and engineers at several institutions with the goal of creating technologies to restore communication, mobility, and independence for people with neurologic disease, injury, or limb loss. The man, identified in the study as T11, is a participant in a clinical trial of a brain-computer interface device that allows him to use a computer cursor and keyboard on a screen. To study whether replay occurs in the human motor cortex - the brain region that governs movement - Rubin, Cash, and their colleagues enlisted a 36-year-old man with tetraplegia (also called quadriplegia), meaning he is unable to move his upper and lower limbs, in his case due to a spinal cord injury. Importantly, says Cash, understanding whether replay occurs with the learning of motor skills could help guide the development of new therapies and tools for people with neurologic diseases and injuries. Cash, co-director of the Center for Neurotechnology and Neurorecovery at MGH and co-senior author of the study. “There’s been an open question in the neuroscience community: To what extent is this model for how we learn things true in humans? And is it true for different kinds of learning?” asks neurologist Sydney S. ![]() However, replay has only been convincingly shown in lab animals. Scientists believe that this replay of neuronal firing during sleep is how the brain practices newly learned information, which allows a memory to be consolidated - that is, converted from a short-term memory to a long-term one. “Then, later on while the animal is sleeping, you can see that those neurons will fire again in that same order,” says Rubin. If a mouse is trained to find its way through a maze, monitoring devices can show that a specific pattern of brain cells, or neurons, will light up as it traverses the correct route. Replay is theorized to be a strategy the brain uses to remember new information. Scientists studying laboratory animals long ago discovered a phenomenon known as “replay” that occurs during sleep, explains neurologist Daniel Rubin of the MGH Center for Neurotechnology and Neurorecovery, the lead author of the study. The study was conducted by Massachusetts General Hospital in collaboration with colleagues at Brown University, the Department of Veterans Affairs, and several other institutions. The findings, published in the Journal of Neuroscience, may help explain how humans form memories and learn, and could eventually aid the development of assistive tools for people affected by neurologic disease or injury. Why do we sleep? Scientists have debated this question for millennia, but a new study adds fresh clues for solving this mystery. ![]()
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