english: Scientists have several theories about what's behind this deterioration, from actual brain shrinkage, the hippocampus  loses 5% of its neurons every decade for a total loss of 20% by the time  you're 80 years old to the drop in the production  of neurotransmitters, like acetylcholine, which is vital to learning and memory.
non_english: Naučnici imaju nekoliko teorija o tome šta je uzrok ovog propadanja, od samog smanjivanja mozga, hipokampus svake decenije gubi oko 5% svojih neurona do konačnog gubitka od 20% do vaše 80. godine, preko pada u proizvodnji neurotransmitera, poput acetilholina, koji je važan za učenje i pamćenje.