Stereotypic route-tracing in experimentally-caged songbirds correlates with general behavioural disinhibition.
Repetitive, unvarying and apparently functionless behaviours called stereotypies are common in caged animals, but the mechanisms of cage stereotypy have remained elusive. We found that stereotypies correlate with a sign of altered brain functioning, the general disinhibition of behaviour, found in stereotyping human patients and animals treated with psychostimulants. We investigated route-tracing stereotypy in blue tits, Parus caeruleus, and marsh tits, P. palustris, caged in a behavioural research laboratory. In experiment 1, stereotypy correlated with disinhibition of responses, shown as persistent responding in extinction learning. In experiment 2a, stereotypy in blue tits correlated with repetitive sequence generation on a ‘gambling task’ that specifically measures disinhibited striatal functioning in humans and correlates with stereotypy in autistic and schizophrenic patients. In experiment 2b, the behavioural disinhibition correlated with stereotypy also affected food-storing behaviour in marsh tits, in particular their response to cache pilfering. In experiment 3, the sequencing of nonstereotypic home cage behaviour was correlated with stereotypy. Finally, changes in stereotypy induced by environmental enrichment correlated with changes in these measures of altered behavioural control. These results suggest that housing conditions that cause stereotypy thus alter many aspects of the behavioural control of caged subjects, mediated by altered striatal functioning. The implications for understanding cage stereotypies in laboratory, farm and zoo animals, and for laboratory-based behavioural experiments, are discussed. We suggest that improving housing conditions so that cage stereotypies do not develop would enhance the validity of laboratory-based behavioural research.