Stereotypy in monkeys and humans.

Stereotyped movements are described in monkeys and humans and are classified as arising from constraint, sensory deprivation in infancy, amphetamine treatment or psychotic states. It is argued that, with the exception of cage stereotypies, stereotyped behaviour is evidence of abnormality in the nervous system consequent upon distorted maturational processes, organic defect or biochemical disturbance. Stereotypy is associated with a state of cognitive inflexibility and social and sensory isolation in humans and monkeys. It is suggested that, while no simple biochemical disturbance in the brain can describe these various occurrences of stereotypy, the cross-species occurrence of a syndrome of isolation, cognitive inflexibility and stereotypy implies a related mechanism mediating these divergent effects. If stereotypy is regarded as a consequence of failure to use sensory input to direct behaviour, therapeutic regimes designed to stimulate responsive behaviours and social interactions are more likely to be effective in the long run than direct attempts to suppress stereotypy.