SRR and memory impairment: Madeira et al. (2015) also found that the levels of D-serine and serine racemase (the enzyme responsible for producing D-serine) in the learning and memory impairment model rats were higher than those in the control group. D-serine can act on N-methyl-D-aspartate receptors, trigger signal transduction in the central nervous system, and also plays an important role in synaptic plasticity, learning and memory (Feng et al., 2013).