BDNF and Cognitive impairment: In pre-clinical studies, hippocampal injection of lenti- or Adeno-associated virus (AAV) carrying brain derived neurotrophic factor (BDNF) 15 or fibroblast growth factor (FGF2) 15,16, respectively, have ameliorated cognitive deficits in AD mouse models, independent of direct modulation of amyloid expression, but by partially increasing clearance of amyloid β peptide and enhancing neurogenesis 17.