Ethologically relevant behavioural assay for investigating reach and grasp kinematics during whole-body motor control in mice

Reach and grasp are critical components of skilled mammalian motor control and their detailed analysis in rodents has been key to deepening our understanding of prehension in the context of health and disease. However, most studies investigating these behaviours focus on isolating forelimb movements with little regard to the whole-body movements that are key for effective behaviour. To address this issue, we designed a novel behavioural approach to investigate reach and grasp during whole-body, vertical locomotion in mice. Using a customizable transparent climbing surface, we show that our behavioural approach can extract key kinematic features of climbing. Mouse climbing gait reflects aspects of quadrupedal locomotion, showing similar phase dependencies on increasing speed, including reduced stance (i.e. grasp) time and duty factor. Analysis of multi-limb coordination indicated that climbing revolves around anti-phasic forepaw movements with less consistency in interlimb coordination in the hindpaws. Fore- and hindpaws also differed in their reach trajectories and velocity profiles. The flexibility of this approach also allows for tailored climbing configurations, which we use to show that mice can adapt to and overcome vertical obstacles. By leveraging naturalistic climbing, our modular behavioural approach enables investigation of complex prehensile behaviours and facilitates new study into the neural circuits underlying whole-body skilled motor control.