BDNF and Alzheimer disease: This hypothesis accords with data from in vitro studies showing that reduction of BDNF in AD is specific to tangle-bearing neurons (Ferrer, et al., 1999; Murer, et al., 1999), and with animal and post-mortem studies showing that the extent of BDNF reduction in the hippocampus was related to the magnitude of cognitive impairment (Connor, et al., 1997; Egan, et al., 2003).