Research in mice led by neuroscientists at Tufts University School of Medicine reveals a new molecular mechanism that is essential for brain maturation and may be used to restore plasticity in aged brains. The study focused on a subtype of inhibitory cell also found in people called Parvalbumin neurons (stained in blue) which exert significant power over the timing of the "critical period" for brain maturation. While previous studies had shown that the short-range synapses (green dots) on these neurons affected critical period opening in the brain's visual cortex (which processes visual scenes), the new study shows that long-range synapses (red dots) on these neurons have a powerful control over critical period closure, despite their lower density in the brain. A molecule called SynCAM 1 stabilizes these long-range synapses, and if SynCAM 1 is removed from these synapses in adult brains, even for a short time, brain plasticity can be restored. This finding could support development of more targeted treatments for human conditions such as autism spectrum disorder and stroke. The research appears in the journal Cell Reports January 8, 2019.