ACTIVE TACTILE EXPLORATION INFLUENCES THE FUNCTIONAL MATURATION OF THE SOMATOSENSORY SYSTEM

1. The hypothesis that active exploration of objects is required for t he functional maturation of neuronal circuits subserving tactile perce ption was tested by subjecting 8- to 11-day old rats to a complete uni lateral section of the facial nerve. This procedure selectively abolis hed whisker protraction movements without affecting the sensory innerv ation of the facial vibrissae, the tactile organs used by rats to disc riminate object texture and shape. 2. Six to 14 mo after the facial ne rve section, simultaneous recordings of neuronal ensembles located in the ventral posterior medial nucleus (VPM) of the thalamus revealed a marked reduction in receptive field (RF) size (in terms of number of w hiskers), and the formation of abnormal RF surrounds, spanning the fac e and contiguous body regions. In addition, the directional organizati on of VPM RFs, represented by caudal to rostral shifts in RF centers o ver 30 ms following whisker stimulation, was greatly reduced in these animals. 3. These results suggest that neonatal active tactile explora tion is required to establish normal spatiotemporal patterning of neur onal RFs within the somatosensory system, and consequently, to develop normal tactile perception.