Behavioural and neural-system analyses of the actions of anxiolytic drugs

Anti-anxiety drugs (including benzodiazepines, barbiturates and alcohol) have a distinctive profile of behavioural action in animal species ranging from goldfish to chimpanzee. This profile may be summarised as a blockade of three kinds of reaction (behavioural inhibition, preparation for vigorous action, and increased attention to the environment) in response to any of three kinds of stimuli (novelty, stimuli associated with punishment, or stimuli associated with frustrative nonreward). On this basis, one may postulate a 'behavioural inhibition system' in the brain, responsible for organising the above reactions in response to appropriate stimuli; activity in this system would then constitute 'anxiety.' One may attempt to describe the brain structures that constitute the behavioural inhibition system either by enquiring about the neurochemical mode of action that is common to anti-anxiety drugs, or by seeking for structures with appropriate behavioural functions. The latter approach has implicated a number of structures in the limbic system (including the hippocampal formation, the septal area, and ascending monoaminergic pathways). Possible information-processing functions of these structures are described.