Supplemental data for: Scars of the past or signs of the present? Investigating persistent stereotypic behaviours in laboratory mice

In conventional laboratory cages, mice frequently develop stereotypic behaviours (SB): repetitive, invariant behaviours with no obvious goal or function. Although transferring mice to enriched environments can reduce SBs, these behaviours do not always decrease, indicating treatment resistance. The Motor Routines Hypothesis predicts that SBs become highly practised motor patterns that are difficult to disrupt, such that resistance will be greatest in mice showing the most frequent, predictable, and routine-like SBs, and in older animals. Alternatively, the Ineffective Enrichments Hypothesis predicts resistance when animals do not value or engage with enrichment, such that mice showing lower preference for enriched housing, less interaction with enrichments, and greater anhedonia will show the least improvement. A related Time Budget Hypothesis predicts that SB reductions simply reflect time spent using enrichment resources. Subjects were 36 sister pairs of female DBA/2 mice, conventionally housed until 12–52 weeks of age. Baseline behavioural observations quantified SB time budgets, and a sucrose preference test assessed anhedonia. One sister from each pair was then transferred to a large, well-resourced cage connected to the original cage, allowing mice to choose where to spend time, while the other remained conventionally housed. Behavioural observations continued for four weeks to quantify changes in SB and assess treatment resistance.