Longitudinal evaluation of open field and string-pulling behaviors in mice

Spontaneous behaviors involve collections of highly organized movement sequences produced on a specific spatial scale. For example, mice exhibit organized movement while establishing a home base in the open field (ambulatory scale) and bimanual coordination while string-pulling (manipulatory scale). Disruptions in the organization of spontaneous behaviors, including home base establishment and string-pulling, have been observed in mouse models of neurological disorders. The influence of age on the organization of these behaviors is yet to be determined. The current study evaluated longitudinal changes in the organization of mouse open field movement under completely dark conditions and string-pulling movement at multiple timepoints from 10 to 20 months of age. Topographic and kinematic characteristics of movement were used to investigate age-related changes in ambulatory (i.e., home base stability) and manipulatory (i.e., reaching consistency) scale movement organization. In the open field, general locomotion and home base measures remained stable. However, changes in heading and movement scaling varied with age. In contrast, string-pulling performance varied in measures of accuracy and kinematics, with general improvements observed with age. These results suggest minimal age-related decline in the organization of spontaneous behaviors. As mouse models are commonly used to model progressive diseases in humans, it is important to consider the translatability of aging. This work provides a foundation to characterize the effect of age and compounding variables (e.g., sleep fragmentation, exercise) on spontaneous behaviors.