Napping for the Win

To further interrogate the underlying neural mechanisms of the cognitive benefits of sleep, Valentin Dragoi, PhD, Rosemary and Daniel J. Harrison III Presidential Distinguished Chair in Neuroprosthetics, and his team used multiple-electrode recordings in areas of the cortex involved in task-related activity to examine the dynamics and information coding in neural populations before, during and after sleep, and their impact on behavioral performance. In a recent study published in Science, Dragoi’s team used multi-electrode intracranial arrays positioned on the head to examine the spiking activity of 4422 neurons recorded across three cortical areas. To define epochs of NREM sleep, the team utilized automated sleep recognition software incorporating all components of polysomnography (PSG) including EEG, electrooculography (EOG), and electromyography (EMG). Evidence shows that brief naps can consolidate memory and improve behavioral and perceptual performance. The team also focused on studying the effects of short sleep periods (30 minutes of rest). They found that increased delta power (2-4 Hz) during slow wave sleep was accompanied by increased synchronized firing in neural population activity in each brain area recorded. Surprisingly, delta-band synchrony in population activity during sleep further caused a desynchronization of neural responses and improvement in perceptual performance during subsequent cognitive tasks. Hypothesizing that the beneficial effects of sleep could be reproduced in their model by electrically stimulating neural populations in the delta-frequency band, they conducted blocks of stimulation for 20 to 30 minutes by generating synchronous electrical pulses in the delta frequency band on eight channels of the electrode array. Remarkably, electrical stimulation of the visual cortex during quiet wakefulness emulated the restorative effects of sleep in the absence of sleep.