Whiskers and barrels: irreversible induction, or ipsilateral maintenance?

Section of the maxillary nerve on post-natal day 3 prevents the formation of barrels in the contralateral sensory cortex, whereas on day 4 the barrels are secure and remain so indefinitely after section of the nerve. The latter result has now been found to be true even if the ipsilateral nerve is cut as well. Thus barrels are irreversibly induced on day 4 by some influence that ascends the contralateral maxillary nerve, and their continued existence after contralateral nerve section is not due to a maintaining influence from the ipsilateral nerve.