ABSTRACT
Organized behaviour requires central neural mechanisms to prevent the simultaneous occurrence of incompatible movements. We investigated neural pathways in crayfish that suppress slow flexion of the abdomen during rapid flexions (‘tailflips’) produced by a separate set of muscles. The slow flexors are innervated in each half segment of the abdomen by five motor neurones and one peripheral inhibitor. In isolated preparations of the abdominal nervous system, stimulation of identified command neurones, which trigger tailflips in intact animals, inhibited spontaneous activity in the motor neurones to the slow flexors and excited the peripheral inhibitor. These effects are mediated by a population of interganglionic interneurones interposed between the command cells and the slow flexor efferents.
Slow flexor reflexes also were inhibited by escape commands. This inhibition includes pathways that act upon early stages of sensory input. As a result, habituation of reflexes, which normally is produced by repeated stimulation, is abolished if each sensory stimulus is preceded by a burst of impulses in the command neurone.
