Activity of thermosensitive neurons of monkey preoptic hypothalamus during thermoregulatory operant behavior.

Unit activities of thermosensitive (TS) and non-TS neurons in the medial preoptic area (MPO) of the monkey were investigated during a high fixed-ratio (FR 12-30) bar press behavior to seek cool air (CT) in a warm environment. The monkey performed the task when ambient temperature (Ta) was raised (35-43 degrees C) and the animal was rewarded with a fall in Ta (23-25 degrees C). The population of neurons which changed the activity at least in one phase of CT was significantly higher among TS neurons (42 of 46) than among non-TS neurons (29 of 64). The most frequently observed responses were the sustained increase or decrease in activity during the bar press period and/or the cooling period. The bar press related activity was not a pure motor coupled response, but its magnitude was greatly modified by the strength of motivation of animals to seek cool air. The cooling phase-related activity was not a thermosensory response which simply reflects the level of skin temperature or its change. It was shown that the response was dependent upon the rewarding value of the cooling air. The results suggest that TS neurons in the MPO may be involved in the control of thermoregulatory cooling behavior.