The brain's global signal fluctuation decreases as the day goes by, a study finds. Does time of day affect brain scans in research and medical testing?

The discovery of why some people are extreme "morning larks" could lead to therapies for inherited sleep disorders and those due to shift work or jet lag.

Altering people's circadian rhythms could help treat a range of conditions. New research on melatonin receptors may be the first step.

If you've just had surgery, researchers have found that you may want to take anti-inflammatories in the morning or at noon, but not at night.

Blue light early in the morning can aid the healing process for mild traumatic brain injury, potentially because it gets people on the right sleep schedule.

"...our work in the monarch could have implications for better understanding seasonal changes in the human brain that could lead to ailments such as seasonal depression."

Stress hormones in the blood have a big influence on the brain's circadian rhythm, according to research in rats.

Our biological clock helps guide our immune system's response to invaders like viruses and cancer, new research with mice indicates.

A new intervention helps teens get more sleep every night. The secret? Earlier bed times and bright flashes of light just before waking.

The right timing and the right temperature makes a bath before bedtime a great way to fall asleep faster and get better sleep.