Repetitive, unvarying, and apparently functionless behaviours called stereotypies are common in caged animals, but to date, the mechanisms of cage stereotypy have remained elusive. Stereotypy is also seen in several human mental disorders, in humans and other animals treated with particular drugs and those suffering particular brain lesions. In all these examples stereotypy is correlated with a pathological disinhibition of behaviour symptomatic of dysfunction in the behaviour selection systems residing in the basal ganglia. We investigated whether cage stereotypy was correlated with psychiatric measures of basal ganglia function; the range of behaviours and experimental paradigms affected by this disinhibition; and whether changes in stereotypy would correlate with changes in measures of basal ganglia function when the behaviour was 'treated' with environmental enrichment.
Experiment 1: we show that stereotypy in caged blue tits (Parus caeruleus) and marsh tits (Parus palustris) is correlated with disinhibition of responses in extinction learning. Experiment 2a: we show that stereotypy in blue tits is correlated with poor performance on the 'gambling task' which measures disinhibited basal ganglia processing in humans, and is correlated with stereotypy in autistic and schizophrenic patients. Experiment 2b: we show that the disinhibition correlated with stereotypy affects food storing behaviour in marsh tits. Experiment 3: we show that the sequencing of non-stereotypic home cage behaviour is similarly disinhibited and disrupted. Finally, changes in stereotypy with environmental enrichment are correlated with changes in measures of basal ganglia function.
These results suggest that housing conditions that cause stereotypy may thus be altering many aspects of the behavioural control of caged subjects. The implications of this for understanding cage stereotypies in laboratory, farm and zoo animals, and for laboratory-based behavioural experiments, is discussed. We suggest that improving housing conditions, so that cage stereotypies do not develop, would enhance the validity of laboratory-based behavioural research.

GARNER, Joseph P.
Animal Science,
University of California
Davis, CA 95616, USA
jpgarner@ucdavis.edu