The Detection of subtle cognitive differences
thesisposted on 27.02.2017, 02:36 authored by Lichtwark, Irene Tatjana
Abstract Background: Physical health and age both influence cognitive functioning. The detection of subtle cognitive differences is particularly important, as these differences might be early indicators of pathological processes. Early detection is central to earlier commencement of treatment. However, few existing measures are available to detect subtle cognitive change within people or difference between people. Aim: This thesis examines the detection of subtle cognitive change in people with Coeliac Disease (CD) and subtle cognitive difference between healthy, elderly people to determine if subtle cognitive difference and change can be detected in the domains of episodic memory, processing speed and response accuracy. These three domains were chosen because previous research has shown that these domains are vulnerable to pathological processes. Methods: In Study 1, 11 participants with CD were administered seven cognitive tests at four time points over the 12 months study period. Blood and duodenal biopsy samples were also obtained at three time points during the first 12 months following the participants’ commencement of a gluten free diet. In the systematic literature review for Study 2, cognitive tests used in 59 publications were reviewed for their ability to detect subtle cognitive difference between healthy people and those with mild cognitive impairment (MCI) in the domains of episodic memory, processing speed and response accuracy. In Study 3, the choice reaction time (CRT) and accuracy (A) scores of the Subtle Cognitive Impairment Test (SCIT), administered to 182 community dwelling, neurologically healthy elderly people (age range from 60 to 89 years), were used to create a performance measure able to detect subtle cognitive differences between the participants. Scores were standardised, and cluster analysis performed to create three performance groups based on subtle cognitive differences in CRT and A. In Study 4, the scores of eight further cognitive tests were examined with non-parametric tests for differences between the three performance groups. Results: For the first time, subtle cognitive improvement in people with CD on a gluten free diet was proven to exist and was measured. The systematic literature review showed that the Hopkins Verbal Learning Test (HVLT) was able to detect subtle cognitive differences, but that too few measures of processing speed and response accuracy were used by the included publications to allow comparison. A performance measure was created that was able to discriminate between good, cautious and impulsive performer profiles based on differences in CRT and A. Significant differences in performance between the three profiles were found in the domains of memory (verbal episodic, semantic memory and nonverbal visuospatial memory), executive functioning (attention and accuracy) and processing speed (decision speed and perceptual speed). Good performers performed better than cautious performers, and these differences were significant in four out of 12 tests and subtests. Cautious performers performed better than impulsive performers in 10 of 12 tests. Relative to good performers, impulsive performers performed significantly worse in nine tests and subtests (p < 0.017). Conclusion: Subtle cognitive change and difference is detectable in people with CD and in the healthy elderly. This ability to detect subtle change and difference can be used to screen and monitor people at risk of health or age related cognitive changes.