Recently, the DSM-5 changed the name of “seasonal affective disorder,” or SAD, to “depressive disorder with seasonal pattern.”
The new name isn’t quite as catchy as “SAD,” but it does describe the condition more precisely.
That’s because depressive disorder with seasonal pattern is not really a distinct disease, but rather depression that worsens at the same time each year, usually in the late fall and winter.
So let’s first review depression. Depression, or major depression, is a serious condition where someone loses their sense of life being enjoyable; this feeling of malaise affects every aspect of their day-to-day life, whether they’re working, studying, eating, or sleeping.
The causes of depression aren’t fully known, but it’s thought to involve a deficiency of monoamine neurotransmitters in the brain, like dopamine, norepinephrine, and especially serotonin.
In depressive disorder with seasonal pattern, there’s a strong relationship with the circadian rhythm, the internal clock that keeps your body in tune with the rising and setting of the sun.
At the base of the brain there’s a region called the hypothalamus, and within it are a group of neurons located in a specific spot called the suprachiasmatic nucleus or SCN.
The neurons in the SCN get information about light from optic nerves, and use that information to run the circadian rhythm.
The SCN relays that information to the pineal gland, a tiny, cone-shaped structure near the hypothalamus.
And when it’s dark out, the pineal gland releases the hormone melatonin, which is chemically related to serotonin.
Melatonin lowers your heart rate and body temperature, helping you go to sleep.