Defects in essential trophic interactions represent one possible explanation for the systems degenerations that occur in Alzheimer's as well as other neurodegenerative diseases. Since a multiplicity of neural pathways are affected in Alzheimer's disease, it is likely that more than one neurotrophic factor may be implicated. Through modern approaches in cell and molecular biology, it may be possible to identify such factors and to more precisely study their role in both sustaining neural connections, and in diseases involving those connections.