Motor activity in the stump of an amputated leg during free walking in cockroaches.

1. A rhythmic pattern of motor activity was recorded in the stump of an amputated leg during free walking in cockroaches. 2. During relatively rapid walking, extensor (depressor) and flexor (elevator) muscles in the intact coxa of the amputated leg showed one burst of activity during each cycle of bursting in an adjacent, intact leg. However, during slower walking these muscles could show two or three bursts of activity during each cycle of bursting in an intact leg. 3. Motor bursts in the stump of an amputated leg showed features similar to those of bursts recorded from intact legs. Burst duration increased with an increase in period, and the bursts generally showed consistent timing (phase) relative to bursts in most of the intact legs. 4. The motor pattern recorded in a stump was very like that recorded in an intact leg during walking, and unlike that recorded during searching for a foothold (defined in the text). It is concluded that after the amputation of most of a leg, motor neurones innervating muscles in the stump of the amputated leg continue to be driven by the interneurones that normally drive the intact leg during walking. Analysis of the motor pattern in the stump may therefore reveal important features of the locomotor control system.