Sleep and Depression

Sleep is not an homogenous phenomenon. It is, of course, divided into sleep both with and without rapid eye movement (REM); Slow and fast electroencephalograph (EEG) wave sleep; sleep with or without muscular tonus. Sleep categories can be discriminated as to whether noradrenalin or serotonin is ascendant. As sleep is divided into dreaming or not, dreaming sleep is subdivided into tonic and phasic. If we include transitory phases, we can increase that division to three as the ancient Hindus did. Divided thus into light sleep, deep sleep and dreaming sleep, these divisions correspond to Vedic categories characterized by the nature of what the sleeper is cognizant. If we make distinctions based on the frequency signature of the EEG, then sleep is divided into four phases. EEG waves are divided into four categories: Alpha, Beta, Delta, and Theta. Wakefulness corresponds to Beta wave activity. Relaxation and drowsiness correspond to Alpha waves. A Hertz spectrum of brainwave frequencies in ascending order begins with the delta waves of deep sleep. The next higher frequency is that of the theta waves of paradoxical sleep. Then there is a .5 Hz gap between the theta frequencies and the frequencies of light alpha wave sleep. The .5 Hz gap between alpha waves and the Beta brain waves of wakefulness is straddled by the frequencies of the anomalous spindles and K complexes of light sleep (Carlson, 2005, Levinthal, 1979).

Light sleep corresponds to slow EEG waves. (Although there are sharp jumps called spindles presented in stage one light sleep.) Light sleep is also characterized by retention of muscular tonus. (The high voltage spikes, characteristic of the phasic portion of dreaming or paradoxical sleep resemble the spindles of light sleep except that they come at a relatively stable rate of 60-70/minute and that they are specifically located in the Pons and the Occipitus.) Slow wave sleep seems to be dependent upon the cortex and thalamus as opposed to the Pons and Occipitus as animals without a cortex fail to present light sleep. Also animals whose brains have been sectioned at the level of the Pons oscillate between deep sleep and dreaming sleep without transitioning through light sleep. Light sleep is correlated with serotonin as injections of serotonin precursors can induce light sleep while artificial serotonin deprivation produces wakefulness (Jouvet, 1967).

EEG frequency decreases as arousability declines indicating a positive correlation. Sleep consists of alternating periods of REM and slow wave sleep. Stage 4 sleep is the time wherein metabolic repair occurs. REM sleep is a time of intense physiological activity despite the lack of muscular tonus. As many as 10% of the population do not present alpha waves. Drugs related to the parasympathetic function of Acetylcholine (ACh) such as atropine present slow waves and arousal in paradoxical simultaneity. Physostigamine, an ACh agonist presents with fast waves and sleep or quiescence. Self reports of dreaming are associated with low amplitude waves indicative of wakefulness during sleep. High frequency asynchronous brain waves and eye movements of 60-70 minutes are also thus associated.

90 minutes after sleep and 45 minutes after stage four EEG enters asynchrony and Theta waves appear. REM begins; muscle tonus disappears perhaps to the point of paralysis punctuated by occasional twitching. People deprived of sleep will recover slow wave and REM sleep but present no need to recover stage one or two sleep. Sleep progresses on a 90 minute cycle containing a 20-30 minute episode of REM sleep. Most stage 3 & 4 sleep occurs early in the night with the proportion of stage 2 sleep increasing as the night progresses. The oscillation between slow wave sleep and paradoxical sleep appears to follow a production and depletion through usage cycles of neurotransmitters perhaps the result of a continually shifting balance of serotonin and noradrenalin similar to the water and oil mixture in a decorative wave machine.

Depression is characterized by disordered sleep. Light transitional sleep is increased at the expense of stage 3 & 4 deep sleep. The sleep of depressed people is punctuated by periods of wakefulness. The first half of their sleep period contains more REM sleep with increased rapidity of the eye movements. Depriving depressed people of either sleep in toto or of merely paradoxical sleep have a positive therapeutic effect resembling that of antidepressant medications. Comparative psychology experiments have demonstrated a connection between monoamine oxidase inhibitors, alleviation of depression, and the suppression of dreams. Like antidepressants, the effects build over time and may continue after discontinuation. Some treatments for depression suppress REM sleep, delaying onset and reducing duration.