Phasic Control of Reflexes During Locomotion in Vertebrates

Abstract

The neural control of locomotion in animals should incorporate mechanisms for coping efficiently with obstacles or painful stimuli occurring at any moment of the loco-motor cycle. These mechanisms would generate patterns of responses best adapted to the current phase of locomotion. Evidence that such mechanisms exist is provided by the following two observations: 1) in chronic spinal cats walking with the hindlegs on a treadmill, touching the dorsum of a foot at swing phase results in a short latency activation of flexor muscles for all joints of that limb. The same stimulus applied at support phase induces, on the contrary, a marked extensor activity. This switch between flexor and extensor responses in synergy with the current locomotor phase was also repeatedly observed with electri-cal stimulation of the skin; 2) similarly, in the spinal dogfish, the same electrical stimulation applied to the tail fin at the midline yields opposite responses according to the phase of swimming. In the right half cycle, the stimulation produces a powerful synergistic contraction on the right side and the reverse in the left half cycle. Discussion follows concerning different neuronal mechanisms possibly responsible for these phase dependent reflex reversals.

Names published in alphabetical order. (Presenter: S. Rossignol.)