Digging behavior is often used to test motor function and repetitive behaviors in mice. Different digging paradigms have been developed for behaviors related to anxiety and compulsion in mouse lines generated to recapitulate genetic mutations leading to psychiatric and neurological disorders. However, the interpretation of these tests has been confounded by the difficulty of determining the motivation behind digging in mice. Digging is a naturalistic mouse behavior that can be focused toward different goals, that is foraging for food, burrowing for shelter, burying objects, or even for recreation as has been shown for dogs, ferrets, and human children. However, the interpretation of results from current testing protocols assumes the motivation behind the behavior often concluding that increased digging is a repetitive or compulsive behavior. We asked whether providing a choice between different types of digging activities would increase sensitivity to assess digging motivation. Here, we present a test to distinguish between burrowing and exploratory digging in mice. We found that mice prefer burrowing when the option is available. When food restriction was used to promote a switch from burrowing to exploration, males readily switched from burrowing to digging outside, while females did not. In addition, when we tested a model of intellectual disability and autism spectrum disorder that had shown inconsistent results in the marble burying test, the Cc2d1a conditional knockout mouse, we found greatly reduced burrowing only in males. Our findings indicate that digging is a nuanced motivated behavior and suggest that male and female rodents may perform it differently.

Digging and burying behavior is often used to test anxiety and repetitive behaviors in mice. Different digging paradigms have been developed and have become popular assays for anxiety, obsessive-compulsive disorder (OCD), and repetitive behaviors in mouse models for multiple psychiatric and neurological conditions. However, the interpretation of these tests has been confounded by the difficulty of determining why mice dig. Digging is a naturalistic mouse behavior, that can be focused towards different goals, i.e. foraging for food, burrowing for shelter, burying objects, or even for recreation as has been shown for dogs, ferrets, and human children. Current testing protocols may focus on one type of digging (burrowing, foraging or burying) or allow the animal to dig freely, but interpretation of the results infers the motivation behind the behavior and often assumes that increased digging is a repetitive or compulsive behavior. We asked whether providing a choice between different types of digging activities would increase sensitivity to assess digging motivation. Here, we present a test to make clear determinations between burrowing and exploratory digging in mice. The test was designed to be rapid (less than 30 minutes) and using simple measures, so that it can be easily implemented with or without automated tracking. We found that mice seem to prefer burrowing when the option is available and asked whether food restriction would cause a switch from burrowing to exploration. While males and females displayed subtle behavioral differences at baseline that did not lead to statistically significant results, males readily switched from burrowing to digging outside, while females did not. In addition, when we tested a model of intellectual disability and autism spectrum disorder that had shown inconsistent results in the marble burying test, the Cc2d1a conditional knock-out mouse, we found greatly reduced burrowing only in males. Our findings indicate that digging is a nuanced behavior and suggest that male and female rodents may perform it differently. We propose that juxtaposing different kinds of digging will increase sensitivity in detecting deficits and will provide a better insight into behavioral differences.

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