A. Cell adhesion related genes: The genes whose products are involved in cell adhesion processes provide a number of especially interesting results (Table I). Cell adhesion mechanisms are central for properly establishing and regulating neuronal connections during development. Cell adhesion mechanisms can play major roles in mnemonic and other neuroadaptive processes in adults [159, 160]. It is interesting to note that most of the cell adhesion related genes that we identify in these genome wide association studies are expressed in developing and adult brains. Altered expression of several of these genes can alter neurite extension [161–163], activate signaling pathways [164–169] and alter mnemonic processes [163]. Almost all of these cell adhesion-related genes are expressed in memory-associated brain regions that include hippocampus and cerebral cortex (http://brain-map.org) [170–173]. By contrast, substantial expression in mesolimbic/ mesocortical dopamine “reward system” neurons is not documented for many of them.
