Adaptive Plasticity in the Spinal Control of Left‐right Coordination During Locomotion

Abstract

Hindlimb (HL) locomotion recovers in chronic spinal‐transected cats following ankle extensors neurectomy (Bouyer et al. 2001), indicating compensatory spinal mechanisms. However, such recovery has only been tested during single‐belt treadmill locomotion at moderate speeds (0.35 m/s to 0.5 m/s). Here, HL locomotion was assessed at several speeds and left‐right speed differences during tied‐belt (equal left‐right speeds) and split‐belt (unequal left‐right speeds) locomotion, respectively, in 4 chronic spinal‐transected cats implanted with chronic electrodes for EMG. Spinal transection was made at the last thoracic segments and cats were trained to recover HL locomotion. A unilateral denervation of the lateral gastrocnemius and soleus was made after stable HL locomotion had recovered, at least 1 month post‐transection. Denervation produced variable results between cats. In the most affected cat, the denervated HL made abnormal contacts with the paw dorsum and left and right HLs were not coordinated 1‐2 days post‐denervation, producing an unstable locomotion. Although the pattern gradually stabilized over several weeks, plantigrade placement of the denervated HL was facilitated only if the non‐denervated HL stepped faster during split‐belt locomotion. In the opposite split‐belt condition, the pattern remained unstable. In the least affected cat, although no abnormal paw placements were observed 1 day post‐denervation, HL locomotion was considerably more stable with the denervated HL stepping faster during split‐belt locomotion. Preliminary results suggest that ankle extensors are important for the spinal control of left‐right coordination and that adaptation can be shaped by split‐belt locomotion.