_ Two distinct patterns in of brain damage predicted by studies one studying how brain circuits wire up structurally in their natural manner and the other their functional connections, converged on a remarkably similar model which predicted the sites of degeneration in each forms of dementia .These studies have been proved significant since the models to predict and study the human neural degeneration has remained elusive.  Neurodegenerative process is thought to involve the accumulation of abnormal toxic proteins and the spread of these toxic proteins between neurons, which may be contagious through their synaptic connections.

http://www.todaysseniorsnetwork.com/diabetes_impact_dementia_brain_patterns.htm

http://www.ncbi.nlm.nih.gov/pubmed/17267521
 
 
_  Studies on Brain imaging suggest that Alzheimer’s and other forms of most prevalent dementia’s may spread within nerve networks in the brain by moving directly between connected neurons, in a way  by propagating in all directions. Studies concluded that a nerve region's connectedness to a disease hot spot trumps overall connectedness, spatial proximity and loss of growth-factor support in predicting its vulnerability to the spread of Alzheimer’s.

http://memory.ucsf.edu/blog/alzheimer%E2%80%99s-disease-spreads-through-linked-nerve-cells-brain-imaging-studies-suggest-522/