From the bench to the bedside: Sleeping when you′re awake, lasers and the blood-brain barrier, neurons with a taste for lactate, and more…

Neurosurgeons, perhaps above all others, are familiar with prolonged periods of wakefulness, routinely sacrificing sleep for the practice of their art. Sleep deprivation is known to have detrimental cognitive effects, and neuroimaging experiments have shown dramatic changes in activation of brain areas. Despite these observations, it is not known how these changes correlate to alterations in neuronal activity. In this study, Vyazovskiy et al., recorded from ensembles of neurons in the deep layers of the frontal motor cortex of awake, behaving rats. After characterizing neuronal activity during spontaneous awake and sleep states, rats were kept awake for prolonged periods of time. They found that the longer the rats were kept awake, the more frequently neuronal activity resembled periods seen during non-rapid-eye-movement (NREM) sleep. These periods, termed “off states,” were characterized by groups of neurons showing brief periods of silence and overall slow activity. Interestingly, when rats were then allowed to sleep, those that were kept awake the longest also had the longest “off states” during sleep as well. When the recording electrodes were moved to other brain areas, similar effects were observed. In animals kept awake the longest, there were periods when all recorded areas went offline, though most of the time the “off states” were local. Within a local cortical region, they found that groups of neurons could go completely silent while others fired normally, suggesting that during sleep deprivation certain neurons “go to sleep” while others remain awake. All of this occurred while the animal was awake! The take-home message: ultimately, regardless of how long you want to stay awake, neuron eventually give up and go offline. The next question: can a cup of coffee wake them back up again?