Early motor activity drives spindle bursts in the developing somatosensory cortex

Sensorimotor coordination emerges early in development. The maturation period is characterized by the establishment of somatotopic cortical maps(1,2), the emergence of long-range cortical connections(3), heightened experience-dependent plasticity(4-7) and spontaneous uncoordinated skeletal movement(8,9). How these various processes cooperate to allow the somatosensory system to form a three-dimensional representation of the body is not known. In the visual system, interactions between spontaneous network patterns and afferent activity have been suggested to be vital for normal development(10,11). Although several intrinsic cortical patterns of correlated neuronal activity have been described in developing somatosensory cortex in vitro(12-14), the in vivo patterns in the critical developmental period and the influence of physiological sensory inputs on these patterns remain unknown. We report here that in the intact somatosensory cortex of the newborn rat in vivo, spatially confined spindle bursts represent the first and only organized network pattern. The localized spindles are selectively triggered in a somatotopic manner by spontaneous muscle twitches(8,9), motor patterns analogous to human fetal movements(15,16). We suggest that the interaction between movement-triggered sensory feedback signals and self-organized spindle oscillations shapes the formation of cortical connections required for sensorimotor coordination.