Medically reviewed by Johnstone M. Kim, MD Key Takeaways The pupil controls how much light enters the eye, allowing for clear ...

For the first time, researchers have been able to observe how the pupils react during sleep over a period of several hours. A look under the eyelids showed them that more happens in the brain during ...

Arousal is a fundamental part of how our brain keeps us alert, engaged, and responsive to the world around us. It is controlled by networks deep in the brainstem, like the locus coeruleus (LC), which ...