The Effect of Limb Amputation On Locomotion in the Cockroach Periplaneta Americana

ABSTRACT The effects of amputating parts of legs on walking in the cockroach Periplaneta americana were studied with the aid of high-speed motion pictures. Amputation of one or two legs at the femoro-tibial joint, leaving the femur to touch the ground and thus provide support during walking, had very little effect on the timing of movements of ipsilateral or contralateral leg pairs, so that gait was constant at nearly all speeds of locomotion. The cycle of forward (protraction) and rearward (retraction) movements of individual legs was also little affected by the amputations. Amputation of combinations of two legs at the trochantero-femoral joint, leaving the animal without the support of the amputated legs, had no effect on the timing of movements of contralateral leg pairs, but had a strong effect on timing between ipsilateral ones, such that gait changed as a function of the speed of locomotion. Except for a general depression in most cases, the ratio of protraction to retraction for each leg at any given walking speed was unchanged. On the basis of these results it is suggested that the timing of leg movements is strongly influenced by feedback from peripheral receptors, while the cycle of protraction and retraction in each leg is largely under central control. A model of this control based on sinusoidal activation and inhibition of muscles of protraction and retraction is presented and discussed.