in lab animals of all ages, environmental enrichment has been related to dendritic branching, spine density, and overall number of synapses. in addition, skill training has been shown to lead to the formation and stabilization of new spines while destabilizing old spines, suggesting that the learning of a new skill involves a rewiring process of neural circuits. since the extent of spine remodeling correlates with success of learning, this suggests a crucial role of synaptic structural plasticity in memory formation. in addition, changes in spine stability and strengthening occur rapidly and have been observed within hours after training.