How Sleep Deprivation Leads to Disrupted Neural Processing
Post by Meredith McCarty
The takeaway
Sleep deprivation leads to changes in sensory perception and arousal levels. The measured increase in neural population synchrony and decreased responses to auditory stimuli are similar across NREM sleep and sleep deprivation states.
What's the science?
Sleep deprivation is known to alter cognitive performance in numerous ways, including the impairment of working memory, vigilance, cognitive speed, and executive attention. Despite the apparent cognitive impairments associated with sleep deprivation, the extent to which sleep deprivation alters neural processing remains underexplored. This week in Current Biology, Marmelshtein and colleagues recorded the auditory cortex of rats during different states of vigilance to determine what changes in neural activity are associated with sleep deprivation.
How did they do it?
A total of 7 adult male rats were implanted with microwire arrays, and EEG and EMG electrodes and placed in a motorized running wheel apparatus for a ten-hour experimental paradigm. The microwire arrays allow for sampling of single neuron spiking activity, whereas the EEG and EMG electrodes allow for monitoring of slower brain rhythms across larger networks, as is relevant for determining arousal state. In order to induce vigilant and sleep-deprived states, the authors programmed the wheel to alternate between 3 seconds of forced running and 12-18 seconds of fixed wheel position over the first 5-hour experimental period. Following this 5 hours of sleep deprivation, the wheel was fixed for the final 5 hours in order to allow for a recovery sleep opportunity. Throughout the experiment, auditory stimuli trains were presented intermittently via speakers throughout the apparatus. This experimental design allows for the comparison of neural responses in the auditory cortex to auditory stimuli across vigilant, tired, and NREM and REM sleep.
What did they find?
The authors compared many features of auditory processing across experimental conditions to determine whether arousal level had any effect on auditory processing. First, they found no significant effect of sleep deprivation on mean frequency tuning, onset responses, and spontaneous firing rate, which suggests that the rats’ arousal state had no effect on these neural responses. However, they found significant differences in population coupling measures, including increased population synchrony, and decreased entrainment to rapid auditory stimuli trains. These results suggest that sleep deprivation significantly affected how correlated individual neuronal firing rate was with the local population. When comparing neural activity during sleep deprivation and the recovery sleep experimental stages, they found that the neural effects of sleep deprivation - specifically increases in population synchrony - were very similar to NREM sleep. This suggests that low-arousal states, such as sleep deprivation and NREM sleep, lead to disrupted cortical processing of faster auditory inputs.
What's the impact?
This study found that sleep deprivation leads to altered neuronal activity in early auditory sensory regions. While many aspects of neural processing were not affected by arousal level, the authors did reveal significant changes in population synchronization measures due to arousal level. The authors found similar increases in population synchronization and disrupted rapid sensory processing in both NREM and sleep-deprived states. These results have practical implications in the accurate monitoring of arousal levels, and theoretical implications in the continued study of how arousal and brain state influence brain activity.