Premature Oviposition Following Operative Interference with the Brain of the Chicken

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Abstract
Following the accidental discovery that electrical stimulation of the hen's preoptic brain induced premature (Ct) oviposition of the terminal egg of a 2-egg sequence, an analysis was made of relationships between times of stimulation and times and frequency of premature (Ct) lay, and, during the period of maximal response to stimulation thus determined, tests were made of the specificity of stimulus and brain region. Preoptic stimulation at 4–25 hr before Ct oviposition induced premature lay. The incidence of response increased fairly regularly from 25 hr (16%) to 7 hr (100%). Tests during the period of maximal response to stimulation showed that the response was not dependent on the passage of current or position of the electrodes, but was dependent only on operative interference with the cerebrum. Pentobarbital anesthesia, administered before the operation, did not block the response to stimulation. Seventy per cent of premature oviposition following preoptic stimulation over a period of 21 hr, and 92% of premature ovipositions resulting from all brain manipulations during the interval in which stimulation was maximally effective, occurred during the period of 10 AM-noon on the morning of expected Ct lay. Eggs laid within this apparently critical period were premature by 2–5 hr. The implied role of an unidentified diurnal physiological process in restricting the period of premature lay is discussed. (Endocrinology74: 193, 1964)