A mouse’s spontaneous eating repertoire aids performance on laboratory skilled reaching tasks: A motoric example of instinctual drift with an ethological description of the withdraw movements in freely-moving and head-fixed mice

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HighlightsReaching movements used by the mouse are complex and depend upon movement freedom and sensory information.The withdraw movement to place food in the mouth is a composite movement, with components expressed depending upon task context.Mouse use rodent-common movements of spontaneous eating to assist in performing skilled reaching tasks.Instinctual drift, the intrusion of natural behavior into the performance of laboratory tasks, aids task performance.Neural coding of movement must be sensitive to the fact that component movements use in laboratory tasks may be part of a natural movement pattern.Rodents display a spontaneous “order-common” pattern of food eating: they pick up food using the mouth, sit on their haunches, and transfer the food to the hands for handling/chewing. The present study examines how this pattern of behaviour influences performance on “skilled-reaching” tasks, in which mice purchase food with a single hand. Here five types of withdraw movement, the retraction of the hand, in three reaching tasks: freely-moving single-pellet, head-fixed single-pellet, and head-fixed pasta-eating is described. The withdraw movement varied depending upon whether a reach was anticipatory, no food present, or was unsuccessful or successful with food present. Ease of withdraw is dependent upon the extent to which animals used order-common movements. For freely-moving mice, a hand-to-mouth movement was assisted by a mouth-to-hand movement and food transfer to the mouth depended upon a sitting posture and using the other hand to assist food holding, both order-common movements. In the head-fixed single-pellet task, with postural and head movements prevented, withdraw was made with difficulty and tongue protrude movements assisted food transfer to the mouth once the hand reached the mouth. Only when a head-fixed mouse made a bilateral hand-to-mouth movement, a component of order-common eating, was the withdraw movement made with ease. The results are discussed with respect to the use of order-common movements in skilled-reaching tasks and with respect to the optimal design of tasks used to assess rodent skilled hand movement.

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