To the Editor.—
In reply to a question about problematic postprandial drowsiness, Dr. Kleitman suggests that the appeasement of hunger as well as stimulus monotony can lead to sleepiness, and prescribes the avoidance of heavy meals, subsequent monotony, and physical inactivity to prevent postprandial sleepiness (219:1486, 1972). Dr. Hauri adds that L-tryptophan intake may increase drowsiness (220:1135, 1972) and suggests avoiding tryptophan-rich foods in the diet, eg, meat and milk.Both of these viewpoints may relate to the same underlying brain mechanisms. Experimental evidence confirms Dr. Kleitman's point, since the electroencephalographic synchrony seen after appetite gratification1,2 is functionally congruent to those electroencephalographic rhythms associated with decreased arousal.3 Increases in brain concentrations of a tryptophan metabolite, serotonin, may cause slow-wave (or "synchronized") sleep4,5; however, the laboratory phenomenon of "postreinforcement synchrony" could be related to any type of gratification, meat-eating included. Drowsiness after sexual activity might provide another example.