SAN FRANCISCO, Aug. 14 — Neuroscientists at the University of California, San Francisco, have discovered that the animal brain reinforces motor skills during deep sleep.
In the study published in Nature Neuroscience, the researchers found that during non-rapid eye movement, or non-REM, sleep, slow brain waves bolster neural touchpoints that are directly related to a task that was newly learned while awake.
Led by Karunesh Ganguly, associate professor of neurology at UCSF, the team implanted electrodes in the motor region of rats’ brains to send electrical signals to a computer, which then drove movement of a detached mechanical device, in a system known as a brain-machine interface (BMI).
Tanuj Gulati, a postdoctoral scholar and lead author of the study, explained in a news release that a particular neuron may normally be devoted to controlling a limb, but a new relationship of that neuron could be created with an external device. The redirected neuron, in this case, will contribute to controlling the external device, and the researchers can track the activity of this neuron to see how the brain integrates this new association.
Gulati and colleagues connected neurons in rat brains to implanted electrodes, which controlled a mechanical waterspout. The source of water was behind a tiny door facing away from the mice. Because the spout faced away, the rats had to learn to use a computer-driven mechanism to move it toward them. As the rats explored several strategies to control the spout, they sometimes activated neurons adjacent to the electrodes. When the proper neurons were activated, the computer moved the waterspout.
“Eventually the rats learn to delink actual movements from the spout – they know they don’t really need to flinch their arm or do anything to make it move,” Gulati was quoted as saying. “All they have to do is volitionally control the pipe and it will come to them.”
The researchers noticed that once rats got the hang of the task while awake, certain neural patterns kept “replaying” during sleep. And these same patterns persisted after the rats woke up, which led over time to improvements in the rats’ performance on the task.
To reveal sleep’s contribution to successful learning, the team used optogenetics, a tool that uses light to turn neurons on or off, to suppress neural activity in a small region of the brain while the rats were sleeping deeply. Because optogenetic manipulations are precisely targeted, there was no change in the structure or amount of sleep, only a relatively small tweak in the firing patterns of the targeted brain cells.
The study confirms that truly task-relevant neural patterns are reviewed during sleep, which enables them to survive after sleep to sharpen motor performance. It is the first evidence to show that neural reactivation and rescaling, namely strengthening and weakening, both happen together during deep sleep.
The findings could lead to new medical stimulation devices, and consumer-driven wearable devices, or “electroceuticals,” which stimulate brain cells and improve learning as people snooze.