REM sleep twitches rouse nascent cerebellar circuits: Implications for sensorimotor development.

The cerebellum is critical for sensorimotor integration and undergoes extensive postnatal development. During the first postnatal week in rats, climbing fibers polyinnervate Purkinje cells and, before granule cell migration, mossy fibers make transient, direct connections with Purkinje cells. Activity-dependent processes are assumed to play a critical role in the development and refinement of these and other aspects of cerebellar circuitry. However, the sources and patterning of activity have not been described. We hypothesize that sensory feedback (i.e., reafference) from myoclonic twitches in sleeping newborn rats is a prominent driver of activity for the developing cerebellum. Here, in 6-day-old rats, we show that Purkinje cells exhibit substantial state-dependent changes in complex and simple spike activity-primarily during active sleep. In addition, this activity increases significantly during bouts of twitching. Moreover, the surprising observation of twitch-dependent increases in simple spike activity at this age suggests a functional engagement of mossy fibers before the parallel fiber system has developed. Based on these and other results, we propose that twitching comprises a unique class of self-produced movement that drives critical aspects of activity-dependent development in the cerebellum and other sensorimotor systems.