BDNF and Alzheimer disease: In humans, BDNF levels have been shown to decrease in brain regions involved in age-related neurodegenerative diseases: e.g., in Alzheimer’s disease (AD) in the frontal cortex (Ferrer et al., 1999), the hippocampus (Phillips et al., 1991), the parietal cortex (Hock et al., 2000) and the entorhinal cortex (Narisawa-Saito et al., 1996).