The Central Interface Between Afferent Temperature Signals and Efferent Drives

Abstract

The concept prevailing in the first half of the 20th century was that the rostral brain stem contains two interconnected centres, one for heat loss, and the other for heat conservation [29,282]. It was replaced, at the dawn of cybernetics, by the model of a single controller: afferent temperature signals, generated at several sites of the body and converging at successive levels of the brain stem, were thought to reach the posterior hypothalamus, where the integration was completed. In the most rigorous version of the single controller, its function was to process a common regulated variable, to compare it to one set-point and to generate a continuous efferent outflow, proportional to the load error and resulting from the difference between regulated variable and set-point. The graded responses to thermal loads were supposed to be accomplished by effector-specific thresholds: a small load error activates behaviour, a medium one additionally alters skin blood flow, and a large one initiates shivering or sweating [185]. However, the evidence presented in chapter 12 argues against a common regulated variable for all effector mechanisms, and separate regulated variables imply separate controllers [427].