BDNF and Alzheimer disease: We then asked if the reason BDNF expression remains strong over the lifespan could be related to GC neuronal activity, because BDNF expression increases with activity (Tongiorgi et al., 2000) and many AD patients and mouse models of AD exhibit increased excitability (Palop and Mucke, 2010; Chin and Scharfman, 2013; Vossel et al., 2017).