The ocular dominance (OD) shift that occurs in visual cortex after brief monocular deprivation (MD) is a classic model of experience-dependent cortical plasticity. It has been suggested that OD plasticity in layer 2/3 of visual cortex precedes and is necessary for plasticity in the thalamocortical input layer 4. Here, we show in mouse visual cortex that rapid OD plasticity occurs simultaneously in layers 2/3 and 4. Remarkably, pharmacological blockade of cannabinoid receptors completely prevents the OD shift in layer 2/3, leaving plasticity intact in layer 4. Thus, experience-dependent cortical modifications in layers 2/3 and 4 can occur in parallel, via distinct mechanisms. These findings simplify the mechanistic description of plasticity in layer 4, force a revision in the interpretation of previous studies in which laminar differences in OD plasticity mechanisms were unrecognized, and have important implications for the therapeutic use of cannabinoid receptor antagonists in humans.