Investigative burying by laboratory mice may involve non-functional, compulsive, behaviour

The burying activity levels of albino mice offered a glass marble and a living scorpion on different occasions, were compared with the levels of exploration/investigation, avoidance, and displacement activities the same subjects performed during these and two other tests, the latter involving exploration with no particular stimulus-object and displacement with locomotion impossible. Although different average response levels were expected to occur in the different tests, it was assumed that the levels of related behavioural patterns correlated over the variation of individual mice. The scorpion elicited more burying than the marble, but the inanimate stimulus-object caused more avoidance. Exploration produced the only consistent, positive, correlation with burying in both female and male subjects. Only negative correlation occurred in males between burying and displacement, suggesting that these were alternative, in part non-functional, patterns. In females and males, while both touching and avoiding the marble decreased with experience over days, burying and displacement did not. The main conclusion is that burying began as an appropriate, investigative, activity, but, following frustrated investigation of the non-reactive stimulus-object, persisted as a compulsive stereotypy in subjects lacking in general experience, as laboratory rodents are in comparison with wild conspecifics. A simple model of compulsive disorder is proposed, in which initially appropriate behaviour goes on with inappropriate repetition when it does not attain its aim and the subject has internal difficulty in finding alternative patterns.