5-HYDROXYTRYPTAMINE AND IMPULSE CONTROL - PROSPECTS FOR A BEHAVIORAL-ANALYSIS

Impulsiveness is a significant clinical problem associated with a vari ety of psychiatric and neuropsychiatric disorders. Clinical and experi mental studies have provided evidence that individuals displaying impu lsive behaviour tend to show signs of deficient functioning of the asc ending 5-hydroxytryptaminergic (5-HTergic) pathways of the brain. A pe rsistent problem in investigations of the biological basis of impulsiv e behaviour has been the lack of a satisfactory definition of 'impulsi veness', as distinct from other behavioural features, such as aggressi on, which are often apparent in 'impulsive' individuals. Research in t he experimental analysis of behaviour suggests that two important char acteristics of 'impulsiveness' are (i) deficient tolerance of delay of gratification and (ii) inability to inhibit or delay voluntary behavi our; both of these characteristics are amenable to study in laboratory animals. We describe some delayed reinforcement and delayed response paradigms which purport to capture these behavioural characteristics, and review recent evidence that manipulation of 5-HTergic function alt ers behaviour in these paradigms. It is argued that the two characteri stics of 'impulsiveness' are themselves the product of disturbance of more fundamental behavioural processes; the nature of these processes is considered.