Cover legend: A summary of the effects of polysialic acid (PSA) and its predominant carrier, the neural cell adhesion molecule NCAM. Deficits in expression of these molecules impair hippocampal long-term potentiation and depression (LTP and LTD) in mice, and are linked to schizophrenia and aging in humans. Accumulating evidence suggests that PSA-NCAM regulates the balance in signaling through synaptic GluN2A versus extrasynaptic GluN2B, and that pathological conditions related to deficiency in PSA or NCAM can be pharmacologically compensated by modulation of GluN receptors. Cover design by Oleg Senkov and Alexander Dityatev. ©NejroN/Bigstockphoto.com—the image of young man; ©Nejron Photo/Fotolia.com—the image of old man. For more information, see the article by Kochlamazashvili et al. (pages 2263–2275).