While it is well known that sleep improves cognitive performance, the underlying neural mechanisms, particularly those related to non-rapid eye movement (NREM) sleep, remain largely unexplored. A new study by a team of researchers from Rice University, the Houston Methodist Center for Restoration of Neural Systems and Weill Cornell Medical College, coordinated by Rice’s Valentin Dragoi, has uncovered a key mechanism by which Sleep improves neural and behavioral performance, potentially changing our fundamental function. understanding how sleep increases intellectual capacity.
The research, published in Sciencereveals how NREM sleep (the lighter sleep one experiences when napping, for example) encourages brain synchronization and improves the encoding of information, shedding new light on this stage of sleep. The researchers replicated these effects using invasive stimulation, suggesting promising possibilities for future neuromodulation therapies in humans. The implications of this discovery will potentially pave the way for innovative treatments for sleep disorders and even methods to improve cognitive and behavioral performance.
The research involved an examination of neural activity in multiple areas of the macaques’ brain while the animals performed a visual discrimination task before and after a 30-minute period of NREM sleep. Using multiple electrode arrays, the researchers recorded the activity of thousands of neurons in three areas of the brain: the primary and middle visual cortices and the dorsolateral prefrontal cortex, which are associated with visual processing and executive functions. To confirm that the macaques were in NREM sleep, the researchers used polysomnography to monitor their brain and muscle activity along with video analysis to make sure their eyes were closed and their bodies relaxed.
The findings demonstrated that sleep improved the animals’ performance on the visual task with greater accuracy in distinguishing rotated images. Importantly, this improvement was exclusive to those who actually fell asleep: macaques that experienced quiet wakefulness without falling asleep did not show the same increase in performance.
“During sleep, we observed an increase in low-frequency delta wave activity and synchronized firing between neurons in different cortical regions,” said first author Dr. Natasha Kharas, a former researcher in Dragoi’s lab and current resident. of neurological surgery at Weill Cornell. “However, after sleep, neural activity becomes more desynchronized compared to before sleep, allowing neurons to fire more independently. This change led to greater accuracy in information processing and performance.” in visual tasks.
The researchers also simulated the neural effects of sleep using low-frequency electrical stimulation of the visual cortex. They applied 4 Hz stimulation to mimic the delta frequency observed during NREM sleep while the animals were awake. This artificial stimulation reproduced the desynchronization effect observed after sleep and similarly improved the animals’ task performance, suggesting that specific patterns of electrical stimulation could potentially be used to emulate the cognitive benefits of sleep.
“This finding is significant because it suggests that some of the restorative and performance-enhancing effects of sleep could be achieved without the need for actual sleep,” said Dragoi, co-author of the study and professor of electrical and computer engineering at Rice, Rosemary. and Daniel J. Harrison III, Presidential Distinguished Chair in Neuroprosthetics at Houston Methodist and professor of neuroscience at Weill Cornell. “The ability to reproduce sleep-like neural desynchronization in an awake state opens new possibilities for improving cognitive and perceptual performance in situations where sleep is not feasible, such as for people with sleep disorders or in extenuating circumstances such as space exploration.” .
The researchers further elaborated on their findings by building a large neural network model. They found that during sleep, both excitatory and inhibitory connections in the brain weaken, but they do so asymmetrically, making inhibitory connections weaker than excitatory connections, causing increased arousal.
“We have discovered a surprising solution that the brain employs after sleep whereby neural populations involved in the task reduce their level of synchrony after sleep despite receiving synchronization inputs during sleep,” Dragoi said.
The idea that NREM sleep effectively “boosts” the brain in this way, and that this reset can be artificially mimicked, offers potential for developing therapeutic brain stimulation techniques to improve cognitive function and memory.
“Our study not only deepens our mechanistic understanding of the role of sleep in cognitive function, but also breaks new ground by showing that specific patterns of brain stimulation could substitute for some of the benefits of sleep, pointing toward a future in which we could improve brain function independently of sleep itself,” Dragoi said.
This research was supported by grants 5R01EY026156 (VD) and 5F31EY029993 (NK) from the National Eye Institute.