Could learning that uses cognitive control to judiciously use relevant information while ignoring distractions generally improve brain function, beyond forming explicit memories? According to a neuroplasticity hypothesis for how some cognitive behavioural therapies are effective, cognitive control training (CCT) changes neural circuit information processing1,2,3. Here we investigated whether CCT persistently alters hippocampal neural circuit function. We show that mice learned and remembered a conditioned place avoidance during CCT that required ignoring irrelevant locations of shock. CCT facilitated learning new tasks in novel environments for several weeks, relative to unconditioned controls and control mice that avoided the same place during reduced distraction. CCT rapidly changes entorhinal cortex-to-dentate gyrus synaptic circuit function, resulting in an excitatory–inhibitory subcircuit change that persists for months. CCT increases inhibition that attenuates the dentate response to medial entorhinal cortical input, and through disinhibition, potentiates the response to strong inputs, pointing to overall signal-to-noise enhancement. These neurobiological findings support the neuroplasticity hypothesis that, as well as storing item–event associations, CCT persistently optimizes neural circuit information processing.