Thermosensitivity of the Goat's Brain

1. Experiments were done in conscious goats to estimate the gain of brain temperature sensors and to evaluate that fraction of the thermosensitivity of the entire brain which can be determined by a thermode located in the hypothalamus. 2. The animals were implanted with local thermodes, carotid loops and intravascular heat exchangers permitting independent control of hypothalamic temperature, extrahypothalamic brain temperature and trunk core temperature. 3. Small and slow ramp-like displacements of hypothalamic temperature generated continuously increasing thermoregulatory responses without any dead band, if a negative feed-back from extrahypothalamic sources was suppressed. 4. The hypothalamic sensitivity determined by the metabolic response to slow ramp-like cooling of the thermode amounted to -1.4 W/(kg degrees C) and equalled approximately 30% of what had been found for total body core sensitivity in another series of experiments. 5. Total brain thermosensitivity was -1.6 W/(kg degrees C), which implies that a large thermode centred in the hypothalamus can detect approximately 85% of the thermosensitivity of the entire brain.