As we slowly move from summer to fall, it may be timely that the issue of Biological Psychiatry that arrived in the mail today is devoted to how the brain’s clock affects mood. It points to growing evidence that part of what drives mood cycles are disruptions in the brain’s daily (circadian) rhythms. It appears that people who are vulnerable to depression have a brain clock that is more easily disrupted.
When the brain’s clock is disrupted many functions of the brain and body no longer work together. The result is fatigue during the day and disrupted sleep at night. These changes in turn affect memory, mood, and even the immune system.
As I have mentioned in other posts, some psychiatrists have even suggested that circadian rhythm disruptions are the central feature of depression and mood cycles. Or, to put it more simply, that depression is basically a sleep disorder… which is probably an oversimplification but does highlight the importance of paying attention to sleep, and light exposure when striving to “live creatively with moods.”
How does this complicated system function?
Basically, light enters your retina, and then signals get sent to the suprachiasmatic nucleus. This tiny part of the brain resets all of the separate clocks in the brain and body that need to be coordinated in order for you to be alert during the day and to sleep well at night.
The Suprachiasmatic Nucleus
The tiny suprachiasmatic nucleus of the hypothalamus is responsible for regulating
all of the circadian (daily) rhythms that function in the brain. It receives information about light from the retina.
The SCN then sends signals via direct and
indirect projections throughout the brain. It
also coordinates the timing of the release of multiple peptides and hormones, including melatonin, which promotes sleep onset.
Interestingly, the SCN seems to regulate the timing of rhythms in the body via alterations in body temperature, which serve as a universal cue to synchronize multiple organ systems to the light/dark
cycle.
Highlighting the importance of circadian rhythms in mood is evidence of how alterations in the brain’s clock affects behavior.
Mice with an abnormal Clock gene act in a way that strongly resembles that of bipolar patients in the
manic state. When these mice are given the mood-stabilizing drug lithium, the majority of their behaviors become more like those of other mice.