Type 2,  the trophic type.  The second sub type of cognitive impairment that Dr. Bredesen recognized is the trophic type.  In medicine trophic means nourishing.  The brain needs nourishment from hormones the body normally makes such as thyroid, estrogen, testosterone, insulin and also from vitamins such as vitamin B12.  When these hormones are missing, as they often are in the elderly, simply replacing those trophic factors leads to a reversal of the cognitive decline and flips the switch back to the neuronal growth side.