Note this shows letters held in working memory ie the letters of the alphabet being held and passed from short term to long term areas by the thing that controls this, ie the hippocampus. This is part of the brain that degenerates quickest year by year after age thirty . This ageing is made worse by nitrous [nitrogen ] oxide in the the blood in wrong amounts. [[See John Hopkins University .Dawson.]] Recently it has been found that the parts of the brain where the letters are held are different places as seen in image These places are the same for people over thirty but for young people growing these sites vary and these sites change and may not be part of the over thirty old persons memory system; eg a teenager may utilise a part of the brain that controls sex drive to store letters as part of the working memory system but when over thirty this region of the brain is not used, eg a year later it may be another part of the brain that is brought into play to make the working memory able to process letters until through time the parts usually used by most people over thirty settle down. ?????This exciting discovery tells us that until about the age of thirty we cannot know except by a special scan which part of the brain in a young adult or child is being used to process letters [ words too] See Nature Magazine. This questions how can anyone explain the use of Ritalin if the parts of the brain are changing their functions at different ages for the same younger adult or child.