The locomotion of the low spinal cat. I. Coordination within a hindlimb.

Kittens were subjected to a complete transection of the spinal cord (Th 10--12) 1--2 weeks after birth. A few days after the operation they could perform alternating limb movements and somewhat later walking movements with their hindlimbs on a treadmill. The stepcycle of the hindlimbs could be divided into a flexion phase (F) and a first (E1), second (E2) and third (E3) extension phase. The duration of the support phase decreased markedly with treadmill velocity while the swing phase decreased to a much smaller extent. The pattern of electromyographical activity in hip, knee, ankle and toe muscles during treadmill locomotion was very similar to that of the intact cat. This related to both the timing and the general shape of locomotor bursts. The extensor muscles were thus activated well before the placement of the foot and able to produce enough force to support the body. The propulsive thrust in each step was, however, decreased and the animals showed more severe deficits particularly in their equilibrium control. It is concluded, however, that neural networks in the spinal cord (with its peripheral inflow intact but without supraspinal influences) have the capacity to generate a specific and detailed locomotor pattern.