From what i understand and reall think the hippocampus does but the only evidence suggest less activity in imaging done of the prefrontal cortex not really shrinage would be the term I would use-- less of activity shown in images scanned --which i believe trying to make this little more simple my oppinion --it comes for from a BDNF gene that has been assoc with a smaller hippcamous --that gene belongs to a family of genes that infulence brain growth ---stimulating it will help from getting worse (not only meds other therapy like tms) and stop damage ---this is what im trying to explain there is no simplified answer --u have to understand more of the the genes the stress hormones and all diseases and aging with the brain. Im sorry there is no clear answer Matt im trying the best way I know how to explain. Some is more proven in parts and like i said its not written in stone. But studies showed damage can be prevented to me which would be my main objective.