Revisiting Concepts of Thermal Physiology: Understanding Feedback and Feedforward Control, and Local Temperature Regulation.

Most experts agree that the dominant mechanism through which body temperature is regulated, under a thermal challenge, environmental or metabolic, is negative feedback control. However, some consider negative feedback to be too sluggish to account for the rapid speed of response. The impression of sluggishness is based on an assumption that the body temperature that is regulated is a core temperature, whereas we concur with those who have concluded that what is regulated is an integrated temperature compiled from inputs from multiple body parts, including the skin. Negative feedback control is supplemented, though, by feedforward control, which is initiated by cues about the predicted magnitude and timing of the thermal challenge. Feedforward control is anticipatory because it can excite thermo-effectors in advance of the thermal challenge impacting on body temperature. Feedforward control is improved by learning but always is supervised by feedback control. There is disagreement about whether the pro-active excitation of thermo-effectors by temperature receptors in the skin occurs by fast feedback control or by feedforward control. We show that skin temperature receptors can provide physiologically meaningful negative feedback within seconds. Both the feedback and the feedforward regulation of integrated body temperature can be modulated by regulation of the temperature of body parts that have special thermoregulatory needs, notably the scrotum.