The present invention relates PirB expression and function in nervous tissue. PirB expressed in neurons acts to restrict plasticity of neural circuits, and/or, restrict competition between circuits with different activity patterns or levels, for cortical representation. Thus, the present invention relates to methods of increasing nervous system plasticity and associated disorders and diseases in a subject comprising administering to the subject an agent which modulates the activity, signal transduction or expression of PirB in neurons of the subject.