Kinematic analyses reveal impaired locomotion following injury of the motor cortex in mice.

Brain injury in the motor cortex can result in deleterious functional deficits of skilled and fine motor functions. However, in contrast to humans, the destruction of cortex and its descending fibers has been thought not to cause remarkable deficits in simple locomotion in quadropedal animals. In the present study, we aimed to investigate in detail how lesion of the sensorimotor cortex affected locomotion ability in mice using the KinemaTracer system, a novel video-based kinematic analyzer. We found that traumatic injury to the left sensorimotor cortex induced several apparent deficits in the movement of contralesional right limbs during treadmill locomotion. The step length of right limbs decreased, and the speed in the forward direction was abrogated in the swing phase. The coordinates and angle of each joint were also changed after the injury. Some of the abnormal values in these parameters gradually recovered near the control level. The number of cFos-expressing neurons following locomotion significantly decreased in the right side of the spinal cord in injured mice, suggesting a role for cortex and descending fibers in locomotion. In contrast, interlimb coordination did not change remarkably even after the injury, supporting the notion that the basic locomotor pattern was determined by intraspinal neural circuits. These results indicate that the motor cortex and its descending fibers regulate several aspects of fine limb movement during locomotion. Our findings provide practical parameters to assess motor deficits and recovery following cortical injury in mice.