During the short, dreary days of winter, some people feel tired and oversleep, they are depressed and irritable and have trouble concentrating. But once spring arrives, they say they feel fine.
4 percent of the American public say they suffer from this seasonal affective disorder (SAD), a type of depression that occurs during the same season each year.
Biologists know that variations in the amount of sunlight a person receives and her or his circadian clock play a role in the disorder and some have proposed that the neurotransmitters serotonin and melatonin may be involved. However, they have not yet identified the underlying neurobiological mechanisms responsible.