The adult cerebral cortex can adapt to environmental change. Using monocular deprivation as a paradigm, we find that rapid experience-dependent plasticity exists even in the mature primary visual cortex. However, adult cortical plasticity differs from developmental plasticity in two important ways. First, the effect of adult, but not juvenile monocular deprivation is strongly suppressed by administration of barbiturate just prior to recording visual evoked potentials, suggesting that the effect of adult experience can be inactivated acutely. Second, the effect of deprivation is less persistent over time in adults than in juveniles. This correlates with the known decline in CREB function during maturation of the visual cortex. To compensate for this decline in CREB function, we expressed persistently active VP16-CREB and find that it causes adult plasticity to become persistent. These results suggest that in development and adulthood, the regulation of a trans-synaptic signaling pathway controls the adaptive potential of cortical circuits. (Contains 7 figures.)