The brain changes with age: it loses about 10% of weight and some large nerve cells wither. Brain scans also show different brain patterns in younger and older people. Different regions of the brains of old people are also less well connected with each other. Such physical changes appear to be related to loss of cognitive and intellectual abilities in the aged, the most obvious being memory.
In a US study of more than 400 people aged 45 to 103, a little more than half were considered to have mild cognitive impairment while the rest had no memory problems. Some of those with mild memory problems also had signs of other difficulty with judgement, problem solving or with personal care, which are typically seen with Alzheimer's disease. Over the 5-year observation period, only 7% of people with no memory problems went on to develop full-blown dementia. In contrast, 20% to 61% of those with mild cognitive impairment developed dementia, depending on the severity of symptoms at the beginning of the study. Of 25 of those who died, an autopsy of brain tissue showed that 24 had a dementing disorder, including 21 cases of Alzheimer's disease.