The iris is a structure behind the transparent cornea of the eye. It has a circular opening called the pupil that changes size in response to the light level. Your pupils are usually the same size as ...

New research suggests that two simple, quantifiable measures -- spontaneous fluctuations in pupil dilation or heart rate -- could enable earlier diagnosis of Rett syndrome and possibly other disorders ...

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 ...