Motivation is understood as a process that moves organisms to engage in particular acts, but its exact status remains uncertain. Various explanations to account for why individuals engage in certain acts have been offered: INSTINCT, DRIVE and AROUSAL have been used to account for motivation in animals, while complex psychoanalytic (see PSYCHOANALYSIS) and psychological processes have been proposed to account for human actions. LEARNING theorists were much concerned to provide accounts of motivation. The DRIVE REDUCTION theory proposed by Clark Hull (1884–1952) suggested that the INCENTIVE behind all behaviour was elimination and avoidance of discomfort. (Early theories concerning human motivation had similarly stressed the importance of hedonism—the maximization of REWARD and minimization of PUNISHMENT.) Hull and others also distinguished between the motivation produced by an internal state of drive (referred to as PRIMARY MOTIVATION) and that produced by the presence of an external STIMULUS (such as food or water) which was referred to as INCENTIVE MOTIVATION. Primary motivation and incentive motivation evidently interact with each other, even in very simple organisms. For example, it was shown that sugar on the chemosensory apparatus of flies always promotes neural activity, but whether or not consummatory actions follow depends on the internal state of the fly.
The neural bases of motivation were once thought to be essentially hypothalamic and were investigated in terms of basic functions: FEEDING, DRINKING, SEXUAL BEHAVIOUR and THERMOREGULATION. The DUAL CENTRES HYPOTHESIS argued that states such as hunger and satiety—the ‘on’ and ‘off’ switches of particular forms of motivation—were controlled by reciprocally acting centres in the HYPOTHALAMUS, but the notion of drive centres has been largely replaced by more distributed processing accounts.
Elements of the LIMBIC SYSTEM—including the hypothalamus—are often assumed to have a fundamental role in motivation (and the related construct of reward) and some have argued that the NUCLEUS ACCUMBENS operates as a LIMBIC-MOTOR INTERFACE, translating motivation into action. In these neural accounts the idea of a CENTRAL MOTIVE STATE is typically present, either explicitly or implicitly. A central motive state is a neural representation of motivation that exists independently of the internal or external stimuli that generate it, and its strength can be used to account for the degree to which a particular activity occurs. However, this begs a fundamental question concerning the status of the term motivation itself. Is motivation an identifiable process with a designated neural system (in the way that vision is for example) and is that process common to all instances of ‘motivation’? Use of the term ‘motivated behaviour’ is one way of circumventing this problem. By specifying a behaviour rather than the state or motivation, one can examine all of the processes involved in that behaviour (feeding for example) and describe sensory mechanisms, cognitive processes, and effector mechanisms that regulate it. Others have attempted to avoid the question by treating motivation as an ATTRIBUTION that individuals use to label their own actions and intentions and, by extension, those of other people and animals. In this formulation, motivation is simply a shorthand way of describing a quality of disparate conditions that need have no underlying unity.
It is realistic to assume that there is no single substrate to motivation, no single NEURON system that must be activated in order to experience it. What has to be accounted for is why certain activities are selected under particular conditions and why their strength varies. An examination of stimulus strength, cognitive processes of LEARNING and MEMORY, and mechanisms of response selection should provide a satisfactory account of behaviour without recourse to additional constructs such as motivation.
