When You're Drowsy, Is Your Brain Partly Asleep?

When we're feeling very tired, we sometimes remark that we're "half-asleep". But is this more than just a figure of speech? A new paper suggests that parts of our brain may actually 'fall asleep' even while we're still awake. According to researchers Jeremy D. Slater and colleagues of the University of Texas, "local sleep" occurs throughout the human brain, with each brain region passing into and out of a sleep-like state over time. What's more, local sleep becomes more and more common in the brain over the course of the day, suggesting that the tiredness we feel at the end of the day may reflect the fact that much of our brain is inactive. Slater et al. studied six patients who'd each had about 100 electrodes implanted in their brains as part of a program of treatment for severe epilepsy. Here's an example of the electrode locations: