Table 2.

Animal models commonly used to investigate aspects of drug reward, reinforcement (abuse) and dependence.

Aspect of drug reward/reinforcement/dependence	Animal model
Model of drug liking (reward)
Reward + contextual association	CPP
Passive development of ‘drug-liking’
Model of drug abuse (psychological dependence)
Reward + contextual association	IVSA meeting the following criteria:
Escalating volitional drug intake	(a) The animals have satisfied the criteria for robust and prolonged drug self-administration (acquisition)
Drug craving	(b) The animals have undergone extinction to eliminate false responders
Model of psychological and physical dependence
Escalating volitional drug intake	IVSA in animals that have either been allowed to self-administer drugs without limits for prolonged periods (e.g. 24 h access for a period of weeks), or IVSA experiments performed in animals that have been rendered physically dependent by administering large doses of drugs to them for prolonged periods.
Drug craving
Pharmacological tolerance
Physical dependence on withdrawal

CPP: conditioned place preference; IVSA: intravenous self-administration.

Drug reward: the psychoactive properties of the substance produce pleasurable experiences that can lead to voluntary escalation of intake and the development of psychological dependence (reinforcement) leading to drug-seeking (craving).

Abuse (psychological dependence): state in which craving for the rewarding effect of the substance produces compulsive and perseverative drug-seeking and taking (reinforcement). In psychological dependence, the balance of motivation is still in favour of the positive effects (reward) over the negative effects (preventing the negative psychological consequences of abstinence (craving)).

Dependence (psychological and physical): escalating substance intake driven by the development of pharmacological tolerance, and in the case of the opiates, physical dependence during periods of withdrawal/abstinence. In substance dependence, the balance of motivation for abuse shifts from positive effects (reward) to negative effects (to prevent the negative consequences of abstinence of psychological dependence (craving) and physical dependence (withdrawal)).