During head/body movements, gaze stability is ensured by transformation of motion-related sensory signals into respective motor commands. Passively induced motion in all vertebrates including amphibians evokes a robust vestibulo-ocular reflex, suggesting an equally important role of this motor reaction during actively induced motion. However, during self-induced movements including locomotion, motor efference copies offer a convenient additional substrate for counteracting retinal image displacements. During such locomotor activity in Xenopus laevis tadpoles, spinal central pattern generator-derived efference copies elicit spatio-temporally specific eye movements, which are functionally appropriate to offset swimming-related retinal image displacements. In addition, passively induced horizontal semicircular canal signals are suppressed, making intrinsic spino-extraocular motor coupling the dominating mechanism for gaze stabilization during locomotion. The presence of functionally appropriate efference copy-driven eye movements in adult frogs with limb-based locomotion suggests that this mechanism might play a role for gaze stability during rhythmic locomotion also in other vertebrates.
Keywords: Efference copy; Extraocular motoneurons; Locomotion; Vestibular system; Xenopus laevis.