Our level of vigilance fluctuates during wakefulness. We may daydream one minute and the next minute we may be intensely focused on a task. How different levels of arousal control the sensitivity of the cerebral cortex to sensory input is still not understood. By directly performing whole-cell intracellular recordings from visual cortical neurons, Pierre-Olivier Polack, postdoctoral fellow in the Golshani lab, has shown that as mice transition from resting to running, the membrane potential of visual cortical neurons becomes more depolarized and less variable, increasing the responsiveness of these neurons to visual stimulation. This allows the signal communicated by visual cortical neurons to stand out from the noisy internally generated activity of the brain. He also showed that norepinephrine release in the visual cortex is essential for shifting the visual cortex into this activated state. These results have important implications for disorders where attention and alertness are impaired.