For example, the outward signs of Alzheimer’s disease (AD) and the degree of brain damage evident at death are not perfectly correlated. Although some nuns had clear brain evidence of AD, they did not display observable cognitive and behavior declines prior to their deaths. Other nuns had only mild brain evidence of AD but showed severe cognitive and behavioral declines.

Interestingly, the sisters who displayed better language abilities when they were young women were less likely to display AD symptoms. This held true regardless of how much brain damage was evident at the time of their death (Iacono & others, 2009). As researcher Diego Iacono (2009) commented, “It’s the first time that we’re shown that a complex cognitive activity, like language ability, is connected with a neurodegenerative disease.”