In this study, we present in vitro and in vivo data elucidating the effects of TH deficiency on hippocampus-specific neuronal development and, as a result of it, on cognitive and memory impairments, as well as the upstream–downstream relevance between Maf and Mef2c in the neural differentiation of hippocampal PV+ interneurons in developmentally hypothyroid mice. The gene discussed is TH; the disease is memory impairment.