Chronobiology

Investors have always known it. Now psychiatrists know it too: Timing is everything.

Chronobiology is the study of rhythmic or periodic changes in biological functions over particular time periods. In the mental health arena, we must be concerned with daily, monthly, and seasonal rhythms. Hormones (messenger molecules released from various glands closely associated with the nervous system, which travel through the blood to reach their target organs) seem to be essential pieces of the chronobiological mechanisms, and will be reviewed in more detail in the next section. In this section, your awareness of the rhythms most important for mental health professionals will be raised. It is my hope that whenever you see a patient with worsening emotional symptoms, you will wonder: Is this tied to a rhythmic pattern? Is this client worse because of the time of year, the time of month, or even the particular time of the day?

Circadian Rhythms

Circadian rhythms are fluctuations that occur within and around the daily 24-hour cycle. Temperature, energy, sleep, arousal, motor activity, appetite, hormones (e.g., thyroid, cortisol, sex hormones, melatonin), and mood all demonstrate circadian rhythms. Abnormalities in these rhythms are apparent in and relevant to the study and treatment of depression, hypomania, mania, and, to a lesser degree, some anxiety disorders panic obsessive compulsive disorders, dissociative disorders.

The Mechanism of Circadian Rhythms

There are two parts to the proposed regulation of circadian rhythms: external cues and internal pacemakers. As a piano player might adjust or entrain his internal rhythm to the beat of a metronome, so the body adjusts its natural, internal rhythm to the beat of the external world. When it works well, we have a masterpiece, but when it doesn’t, life loses its rhythm.

The external metronome or cues (chronobiologists call them ‘zeitgebers’) include light, temperature, mealtimes, social interactions, posture, and activity levels. The internal pacemaker in the brain that regulates the daily rhythms is called the suprachiasmatic nucleus (SCN). As the name implies, this nucleus sits above (supra) the nerves that emanate from the retina of the eye. The SCN is one of the many nuclei of the hypothalamus, the central integrating station that controls hormonal and autonomic nervous system output.

The neurons in the SCN are stimulated by glutamate, an excitatory neurotransmitter, and GABA, an inhibitory neurotransmitter. Dopamine is also involved in this neural circuit. The external environmental cues lead to activation or inhibition of the SCN, which then causes the pineal gland of the brain to increase or decrease the release of the hormone, melatonin. Melatonin is thought to play a role in the sleep-wake cycle, adjusting the body clock (SCN) via a negative feedback loop, according to the external light cues.