Mandibular movement trajectories and masticatory muscle activities in the rabbit in the sleep and wake states.

Jaw movements and masticatory muscle activities were recorded in freely moving rabbits. During 5 hours of continuous recording, three states were recognized, namely, sleep, rhythmical jaw movements, and wake without any major jaw movements. The rhythmical jaw movements included chewing, drinking, and grooming and were similar in characteristics to those recorded in immobilized animals. During sleep, two kinds of masseter muscle behaviors with jaw movement features were recorded: one characterized by a short EMG bursts and a pause in jaw movements, considered similar to clenching, and the other characterized by cyclic bursts and lateral jaw excursion, a grinding-like movement. The latter was correlated with light sleep, thus suggesting a resemblance between the grinding-like behavior and bruxism.