Loss of ErbB3 signaling in oligodendrocytes during the critical period for myelination mimics the effects of social isolation. (A to D) When Cre-mediated ErbB3 knockdown in oligodendrocytes begins at P19 (Cre+), by P65 mice have (A) reduced mPFC MBP and MAG expression (n = 7 per group); (B) reduced myelin thickness (Cre−; n = 3, Cre+; n = 4), (C) altered sociability, and (D) altered working memory (Cre−; n = 15, Cre+; n = 14). (E to H) No effects were observed when tamoxifen was injected starting at P36 (mRNA measurement: Cre−; n = 4, Cre+; n = 5; myelin thickness: n = 3 for, behavioral tests: Cre−; n = 13, Cre+; n = 12). *P < 0.05, **P < 0.01, ***P < 0.001. Error bars, SEM.