Electromyographic analysis of goal-directed grasping behavior in the American lobster

Animals spontaneously initiate goal-directed behavior including foraging action based on their appetitive motivation. The American lobster Homarus americanus exhibits grasping behavior with its crusher claw as feeding behavior that can be initiated after appropriate operant conditioning. In order to quantitatively characterize the goal-directed grasping behavior with a time resolution fine enough for neurophysiological analysis of its initiation and control mechanisms, we made simultaneous electromyographic (EMG) recording from grasping- and reaching-related muscles of the crusher claw while animals initiated grasping behavior. We developed an in vivo extracellular recording chamber that allowed the animal under a semi-restrained condition to perform operant reward learning of claw grasping. Three muscles in the crusher claw (propodite-dactyl closer/opener and coxal protractor) were found to be closely associated with spontaneous grasping behavior. In spontaneous grasping, the activation of those muscles consistently preceded the grasping onset time and exhibited different activity patterns from the grasp induced by a mechanical stimulus. Furthermore, we found that the timing of coxal protractor activation was closer to the grasp onset and its activity was briefer for goal-directed grasping behavior in trained and hungry animals than for non-goal-directed spontaneous grasping behavior in naive or satiated animals. It is suggested that the goal-directed grasping behavior of lobster is characterized, at least partly, by experience-dependent briefer activity of specific muscles involved in reaching action.