Regenerative therapy for improving memory in aged individuals: Tryptophan, an essential amino acid and precursor of the neurotransmitter Serotonin and the sleep hormone Melatonin, increases Tissue inhibitor of metalloproteinases 2 (TIMP2) levels, improves cognition, and decreases age-associated decline in memory and learning, via down regulation of its target genes, 13/March/2018, 10.45 pm