Motivation Explained

Abstract

A theory of motivation is described in which rewards modulated by motivational states provide the goals for instrumental actions. The “ultimate” (evolutionary adaptive) value of the design principle is that genes specify the goals for actions, and not the actions themselves which can be learned. The “proximate” mechanisms underlying motivation are described with respect to the motivational system underlying hunger which modulates the appetite for the goal value of a food. In primates, including humans, the primary taste cortex in the anterior insula provides separate and combined representations of the taste, temperature, and texture of food in the mouth independently of hunger and thus of reward value and pleasantness. One synapse on, in the orbitofrontal cortex, these sensory inputs are for some neurons combined by associative learning with olfactory and visual inputs, and these neurons encode food reward value in that they only respond to food when hungry, and in that activations correlate linearly with subjective pleasantness. Cognitive factors, including word-level descriptions, and selective attention to affective value, modulate the representation of the reward value of taste, olfactory, and flavor stimuli in the orbitofrontal cortex and a region to which it projects, the anterior cingulate cortex. These food reward representations are important in the appetite for food. Hunger and satiety signals reflecting many gastrointestinal and hormonal processes are integrated in the hypothalamus, and then modulate the reward value of food in the orbitofrontal cortex. Individual differences in these reward representations may contribute to obesity.