Effects of Afference Sign Reversal on Motor Activity in Walking Stick Insects (Carausius Morosus)

Open Access
Publisher Website
Google Scholar
Abstract
The apodeme of the femoral chordotonal organ of a middle leg can be moved from its normal position close to the extensor tendon and inserted into a clot cut in the flexor tendon. This inverts the output of the sense organ and produces a ‘wrong’ afference. During walking on a pair of light wheels the operated leg either makes walking steps or is raised and extended in a ‘salute’ posture. The coordination is similar to that for an intact animal if the operated leg walks but changes to the middle leg amputee timing when the operated leg ‘salutes’. The transitions between saluting and the normal walking behaviour of the operated leg can be explained if it is assumed that the animal depends heavily upon the C.O. for determining the tibia position during both walking and the saluting behaviour. Motor output to the levators and depressors of the femur and the protractors and retractors of the coxa shows bursting activity during the salute at the frequency of 3–4 Hz. The depressor bursts are also modulated at a frequency of ∼ 1 Hz and produce strong regular depressions of the femur which are co-ordinated with the movements of the other legs. The maintenance of regular depressor contractions during the salute shows that an important part of the motor output to the saluting leg (depressor activity) arises from an internal oscillation or rhythmic command which maintains its co-ordinated activity when the normal peripheral sensory input to the leg it is attempting to operate is absent. Retractor activity wanes during the salute suggesting that propulsion is much more dependent upon peripheral input than is the support musculature (depressors), The creation of a ‘wrong’ afference can be used to map the importance of the operated organ in different sub-units of behaviour.