Developmental onset of a cerebellar-dependent forward model of movement in motor thalamus

Summary To execute complex behavior with temporal precision, adult animals use internal models to predict the sensory consequences of self-generated movement. Here, taking advantage of the unique kinematic features of twitches—the brief, discrete movements of active sleep—we captured the developmental onset of a cerebellar-dependent internal model. Using rats at postnatal days (P) 12, P16, and P20, we compared neural activity in two thalamic structures: the ventral posterior (VP) and ventral lateral (VL) nuclei, both of which receive somatosensory input but only the latter of which receives cerebellar input. At all ages, twitch-related activity in VP lagged behind movement, consistent with sensory processing; similar activity was observed in VL through P16. At P20, however, VL activity precisely mimicked the twitch itself, a pattern of activity that depended on cerebellar input. Altogether, these findings implicate twitches in the development and refinement of internal models of movement.