The development of skilled walking in the rat.

The rat is an altricial species and consequently undergoes considerable postnatal development. Careful analysis of the emergence and disappearance of motor behaviours is essential to gain insight into the temporal pattern of maturation of motor system structures. This study presents a qualitative analysis of the developmental progression of skilled movement in the rat by using a skilled walking task. A new rung bridge task was used to expose rat pups to a novel environment in order to reveal their potential capabilities. Ten rat pups were filmed daily from postnatal day 7 through postnatal day 30 as they explored the rung bridge task. Discrete changes in skilled and non-skilled walking in fore- and hind-limbs were evaluated by scoring seven categories and 24 subcategories of motor behaviour, including limb flexion and extension, coordination, posture, sensorimotor responses, distal control, and tail use in rat pups. Frame-by-frame analysis of ambulatory movement revealed six distinct stages of locomotor development. The most significant transformation to mature gait patterns was found between postnatal days 15 and 19, and maturation of all motor behaviour was completed by postnatal day 27. The findings are discussed in relation to the maturation of underlying structures and their relevance to studies of brain damage.