Motor pattern changes during central compensation of eyestalk posture after unilateral statolith removal in crayfish

Electromyographic recording was used to study how the activity of the eyestalk motor system is modified during the recovery of eyestalk posture following unilateral statolith removal in crayfish Procambarus clarkii Girard. Intact animals showed bilaterally balanced activity of the muscle 12 (eyecup-up muscle) in the upright body position. Body rolling caused an increase in the muscle activity on the lowered side and a decrease on the lifted side. Unilateral statolith removal caused imbalance in the bilateral muscle activity in the upright body position: the muscle 12 activity decreased tonically on the operated side and increased on the opposite side. Body rolling of the operated animal caused an increase in the muscle activity from the unbalanced level on the lowered side and a decrease on the lifted side. When the operated animal recovered its original symmetrical posture of eyestalks 14 days after operation, the muscle activity was found on both sides to return to the previous level observed before statolith removal, regardless of the post-operative condition in which the animal was maintained. In those animals that did not recover the original eyestalk posture, the unbalanced activity of bilateral muscles that was caused by unilateral statolith removal remained unchanged. The results indicate that the recovery of eyestalk posture is based on restoration of the original activity balance, rather than on fixation of the operation-induced activity imbalance, among bilaterally homologous sets of muscles in the course of central compensation.