Nature of the early sensory input during the critical period of somatosensory system development
Sensory input plays critical roles in the development of the somatosensory cortex during the neonatal period. This early sensory input may involve stimulation arising from passive interactions with the mother and littermates but also sensory feedback arising from spontaneous infant movements. Relative contributions of these mechanisms under natural conditions remain largely unknown, however. Here, we used simultaneous high speed video recordings of whisker movements and extracellular multichannel silicone probe recordings of cortical barrel column activity. We show that in the whisker related barrel cortex of neonatal rats, spontaneous whisker and whisker pad movements and passive stimulation by the littermates cooperate, with comparable efficiency, in driving cortical activity. Both tactile signals arising from the littermate’s movements under conditions simulating the littermate’s position in the litter, and spontaneous whisker movements efficiently triggered bursts of activity in barrel cortex. Yet, whisker movements with touch were more efficient than free movements. Comparison of various experimental conditions mimicking the natural environment showed that tactile signals arising from the whisker movements with touch and stimulation by the littermates, support: (i) twice higher level of cortical activity than in the isolated animal, and (ii) three times higher level of activity than that supported by the deafferentated thalamocortical oscillator. Altogether, these results indicate that endogenous (self-generated movements) and exogenous (stimulation by the littermates) mechanisms cooperate in driving cortical activity in the newborn rats and point on the importance of environment in shaping cortical activity during the neonatal period.