Relationship between Cognitive Reserve, Cognitive Functioning and Brain Volumetry in Non-Demented Older Adults. Doctoral Thesis

Abstract

The aim of this study was to investigate the cognitive and neural correlates of cognitive reserve in healthy adults. The study tested four hypothesis: (1) higher levels of education, active employment and active daily lifestyle will be associated with better memory performance and higher scores of verbal fluency in healthy adults, (2) higher cognitive reserve will be associated with better cognitive performance in memory, information processing speed, visuo-spatial abilities, executive functions and language abilities in healthy older adults, (3) higher cognitive reserve will be associated with larger brain volume, especially in brain regions considered more vulnerable to ageing and dementia and (4) changes in cognitive performance over time will be associated with the baseline cognitive reserve score. The first hypothesis was tested in a partially representative sample of 546 practically healthy Latvian speaking adults (Mage = 70.54, SD = 10.19, 37.2 % male). Secondary data on education, current employment and leisure were used as proxies for cognitive reserve, memory was assessed using a ten-word memory task and verbal fluency was assessed using semantic verbal fluency task. To better understand the relationship between variables, structural equation model was prepared and tested. Education, employment status, cognitive leisure activities and moderate physical activities were good predictors of the aforementioned cognitive functions, showing a good model fit (?2(7) = 30.837, CFI = 0.970, RMSEA = 0.079, SRMR = 0.058). The second hypothesis was tested in a sample of 61 Latvian speaking practically healthy older adults (Mage = 72.19, SD = 5.02). Cognitive reserve was measured using Cognitive Reserve Index questionnaire (Nucci et al., 2012), working memory, associative memory, processing speed and vocabulary was assessed with Woodcock-Johnson III: Tests of Cognitive Abilities (Paleja, 2006), short- and long-term memory measures were obtained with The Ten-word Memory test (Luria, 1976), reaction time was assessed using the Handball goalie reaction test and data on executive functions and visuo-spatial abilities were obtained using three subtests from Montreal Cognitive Assessment Scale (Nasreddine et al., 2005). Higher scores of cognitive reserve and its sub-indices – education and occupation – were associated with better short-term memory performance, larger vocabulary (CRI-Education) and higher verbal fluency scores and faster reaction times (CRI-Occupation). The results were partially compliant with the results from the larger sample. The third hypothesis was tested in a sample of 58 Latvian speaking older adults (M = 72.19, SD = 5.02, 23.9 % male). Magnetic resonance imaging (MRI) data were obtained with Siemens 1.5 Tesla Avanto MRI scanner (Siemens, Erlangen, Germany) and analysed with Freesurfer 7.2. software. Results partially confirmed the hypothesis, showing that higher occupational achievement and higher cognitive reserve in general were associated with larger cortical volume in left hemisphere middle temporal gyrus, bilateral inferior temporal gyrus, left hemisphere inferior parietal gyrus and right hemisphere pars orbitalis; however, there were no statistically significant associations between cognitive reserve and hippocampus and thalamus (p > 0.05). The final hypothesis was that the changes in cognitive performance over time will be associated with the baseline cognitive reserve score. This hypothesis was tested in a sample of 23 women 68–83 (M = 74.13, SD = 4.70) drawn from the participant pool from the previous study. Same measures for cognitive reserve and cognitive function were used. The mean years between the testing were 3.391 (SD = 0.656). Statistically significant changes were found only in three measures – long-term memory, reaction time composite and clock drawing task. Out of these, only changes in the reaction time were associated with cognitive reserve, specifically – leisure activities, thus only partially confirming the hypothesis. Overall, results indicate that higher cognitive reserve could be associated with better performance in short- and long-term memory, verbal abilities and reaction time even in healthy older adults. Similarly, higher occupational requirements and cognitive reserve as such could also be associated with larger cortical volume in temporal, parietal and frontal regions, thus providing protection against brain atrophy. Finally, changes in cognitive functioning over time, could be associated with active leisure; however, studies in a larger sample are needed.