Li-Huei Tsai, a neuroscientist at MIT, investigates how changing gene expression in the brain can affect memory. To fit inside the nuclei of neurons and other cells, DNA wraps tightly around spherical proteins called histones. For years, Tsai’s group has studied enzymes called histone deacetylases, or HDACs, which silence genes by removing chemical structures called acetyl groups from histones.  In 2012, she found that one such enzyme–called HDAC2–was in overdrive in a mouse model of Alzheimer’s disease, silencing genes important for learning and memory. But blocking HDAC2 allowed these genes to turn on, reversing Alzheimer’s symptoms in mice.