Myelin is known to bind many different axonal growth inhibitors that prevent plasticity seen in critical periods. The Nogo Receptor is expressed in myelin and binds to the axonal growth inhibitors Nogo and MAG (among others), preventing axon growth in mature, myelinated neurons. Instead of affecting the timing of the critical period, mutations of the Nogo receptor prolong the critical period temporarily. A mutation of the Nogo receptor in mice was found to extend the critical period for monocular dominance from around 20 – 32 days to 45 or 120 days, suggesting a likely role of the myelin Nogo receptor in critical period closure.