The control of the rocking movements of the phasmidCarausius morosus Br.

Summary1.Recordings are made from the flexor tibiae muscle (electromyogram) and from the extensor tibiae nerve of freely moving stick insects.2.During rocking of intact animals the flexor and extensor tibiae burst in an alternating, rhythmical pattern (Fig. 5).3.The following sense organs are eliminated: The receptor tendon which is part of the transducer of the femur-tibia-control system is cut. The coxal and trochanteral hair fields, some of which control the coxa-trochanter joint are shaved. The campaniform sensillae which are thought to be involved in controlling the coxa-trochanter joint are destroyed. These operations, which are done in one, three or in all six legs of a stick insect, in general do not prevent the insect from rocking (Fig. 8). But the rocking periods are shorter than in intact animals. A rhythmical alternating bursting pattern can always be observed even during short rocking periods. The frequencies of the oscillations during the rocking periods are changed significantly by these operations. Intact animals rock with a mean frequency of 1.85 Hz. Stick insects with receptor tendons cut, hair fields shaved and campaniform sensillae destroyed in all six legs possess a mean rocking frequency of 3.6 Hz (Fig. 9).4.Changing the normal negative feedback of the femur-tibia-control system into a positive one can be done by transfering the attachment of the receptor tendon from a dorsal to a ventral position relative to the femur-tibia joint axis. This increases the duration of the flexor bursts.5.From the results it is concluded, that a central program underlies the rocking behaviour. The central oscillator can be influenced by sensory feedback. Its eigen frequency (natural frequency) must be high as it is damped by input from the afferences until the frequency observed lies in the range of the “resonance frequency” of the femur-tibia-control system. Perhaps also the control system of the coxa-trochanter joint possesses a resonance frequency within this range.