This study was undertaken to define the role sensory input plays in shaping representational maps in the developing motor cortex. To this purpose the representation of vibrissa movements was examined in adult rats that underwent unilateral deafferentation of a vibrissal pad two days after birth. In 5 newborn rats the infraorbital nerve was cut and the two stumps were glued to promote reinnervation. In other 5 animals the nerve was ligated and cut, then the proximal stump was covered with acrylic glue to prevent reinnervation. Other 5 animals were studied as a sham and 5 as a control experiment. Under ketamine anaesthesia (100mg\Kg i.p.), movements evoked by intracortical microstimulation (ICMS) of the motor cortex contralateral to deafferented vibrissa were mapped in each animal. The ICMS (30 ms trains of 0.25 ms cathodal pulses at 350 Hz, stimulation current ≤60 μA) was delivered at a depth of 1.5mm from the pial surface using glass-insulated tungsten microelettrodes (impedance:0.6-1.2MΩ). The shapes and sizes of vibrissae motor representation in the reinnervation group were not significantly different from those in control and sham group (mean size in reinnervated:3.85±0.4mm2 vs. control:4.45±0.7mm2;p=0.14;t-test). In the persistently deafferented group, a significant shrinkage of the vibrissal motor representation was observed (mean size in deafferented:2.65±0.5mm2 vs. control:4.45±0.7mm2;p=0.002;t-test). These data show that the temporary suppression of sensory input early in life does not affect the shaping and size of vibrissal motor representation in the adult motor cortex. Abnormal shapes and sizes of vibrissal motor representation result from persistent deafferentation early in life.
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