A recent study conducted by Rice University and Houston Methodist has found that nonrapid eye movement (NREM) sleep significantly enhances cognitive performance by synchronizing neural activity and improving information encoding.

The research involved macaques performing a visual discrimination task before and after a 30-minute NREM sleep period, revealing that those who slept showed improved accuracy in distinguishing rotated images compared to their awake counterparts.

This study, published in the journal Science and funded by National Eye Institute grants, was coordinated by Valentin Dragoi and featured key contributions from Dr. Natasha Kharas.

Dr. Natasha Kharas, the first author, noted that during sleep, there was an increase in low-frequency delta wave activity and synchronized neuron firing, which contributed to improved information processing after sleep.

The findings suggest that during sleep, inhibitory connections in the brain weaken more than excitatory ones, leading to increased excitation and a desynchronized state of neural circuits post-sleep.

This desynchronization allows neurons to fire more independently, which is correlated with enhanced information encoding in neuronal populations and improved task performance.

Post-sleep activity was characterized by decreased synchronization compared to pre-sleep, indicating a shift to a more desynchronized cortical state that enhances cognitive function.

The researchers also simulated the effects of NREM sleep using 4-Hz electrical stimulation of the visual cortex while the animals were awake, replicating the cognitive enhancements observed after sleep.

While sleep is known to significantly enhance behavioral and cognitive performance, the exact mechanisms behind these improvements remain partially understood.

Computational models proposed that the observed changes in neural activity could be explained by an asymmetric reduction in synaptic conductance, particularly affecting inhibitory synapses.

Overall, the study indicates that sleep not only synchronizes brain activity but also asymmetrically weakens inhibitory connections, leading to improved cognitive function.

Funding for this important research was provided by National Eye Institute grants 5R01EY026156 and 5F31EY029993.