Myoclonic Twitching and Sleep-Dependent Plasticity in the Developing Sensorimotor System.

As bodies grow and change throughout early development and across the lifespan, animals must develop, refine, and maintain accurate sensorimotor maps. Here we review evidence that myoclonic twitches-brief and discrete contractions of the muscles, occurring exclusively during REM (or active) sleep, that result in jerks of the limbs-help animals map their ever-changing bodies by activating skeletal muscles to produce corresponding sensory feedback, or reafference. First, we highlight the spatiotemporal characteristics of twitches. Second, we review findings in infant rats regarding the multitude of brain areas that are activated by twitches during sleep. Third, we discuss evidence demonstrating that the sensorimotor processing of twitches is different from that of wake movements; this state-related difference in sensorimotor processing provides perhaps the strongest evidence yet that twitches are uniquely suited to drive certain aspects of sensorimotor development. Finally, we suggest that twitching may help inform our understanding of neurodevelopmental disorders, perhaps even providing opportunities for their early detection and treatment.