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The Nun Study is a longitudinal investigation of aging and Alzheimer's Disease. The participants are members of the School Sisters of Notre Dame religious congregation. American sisters born before 1917 were asked to join the study between 1991-1993. The participants agreed to donate their brains for study after death. In a subset of participants, a study was conducted to explore the relationship between linguistic ability in early life to changes in cognition and the development of Alzheimer's disease in later life. All 93 participants in the study were white and born in the US.
To assess linguistic ability, the investigators used handwritten autobiographical submissions by the sisters, written by the nuns after 4 years training at the convent. The documents obtained from the archives were carefully analysed and indices of linguistic ability were developed. One of these was the term "Idea Density (IDs)". This was quantified as the average number of propositions expressed per 10 words. Based on their ID scores, the participants were categorised into 2 groups (LOW and HIGH).
Within the period of the study, there were 14 deaths. Autopsies were done to correlate brain changes with early linguistic ability. Since the sample size was small, another 11 sisters from other convents in the same area were included. There were autobiographical submissions available for those 11 which were subjected to the same analysis. Given below are the data from all the 25.
Neurofibrillary Tangles in Different Regions of the Brain by Linguistic Ability Demonstrated in Autobiographies written in early Life
Idea Density Mean number of Neurofibrillary tangles per 0.586 mm2 Temporal Lobe Parietal Lobe Frontal Lobe Subiculum CA1 LOW (n=10) 9.4 6.2 6.0 22.7 15.8 HIGH (n=14) 0.5 0.3 0.3 3.8 4.8
(1) Neurofibrillary tangles are an indication of Alzheimer's Disease
(2) The subiculum and CA1 form part of the hippocampus. The rest of the regions described are neo-cortical areas.
This problem as well as the companion one (following) were used to explore the diverse approaches taken to study the problem of dementia. In both cases, I used published data.