Glutamate [NMDA] receptor subunit epsilon-2, also known as N-methyl D-aspartate receptor subtype 2B (NMDAR2B or NR2B), is a protein that in humans is encoded by the GRIN2B gene. NR2B has been associated with age- and visual-experience-dependent plasticity in the neocortex of rats, where an increased NR2B/NR2A ratio correlates directly with the stronger excitatory LTP in young animals. This is thought to contribute to experience-dependent refinement of developing cortical circuits. Engineered to overexpress GRIN2B in their brains, mice and rats exhibit improved mental function. The "Doogie" mouse performed twice as well on one learning test.