1 Subjective Cognitive Concerns, Neuropsychological Test Performances, and Frontoparietal Thickness and Connectivity in High-Functioning Older Adults

Abstract

Objective:Neuropsychologists have difficulty detecting cognitive decline in high-functioning older adults, in whom substantially greater neurological change may need to occur before performance on cognitive tests are low enough to indicate cognitive impairment. For high-functioning older adults, subjective cognitive concerns (SCC) may indicate decline that is not detected by the presence of low cognitive test scores but may be related to the absence of high scores and the presence of latent neurological changes. We hypothesized that high-functioning older adults with SCC would have fewer high scores than those without concerns, but a comparable number of low scores. These findings would indicate that objective decline has occurred but would not be detected by a traditional focus on low scores. We also hypothesized that SCC would be associated with lower frontoparietal network volume, thickness, and connectivity, indicating latent neurological change underlying subjective cognitive concerns.Participants and Methods:Participants from an imaging sub-study of an ongoing longitudinal aging study were selected if they had high estimated premorbid functioning, defined as either (a) estimated intelligence >75th percentile on the North American Adult Reading Test (n=48) or (b) having a college degree (n=62). This resulted in 68 participants subdivided based on SCC, defined as one or more self-reported SCC on the Medical Outcomes Study Cognitive Functioning Scale (MOS-Cog). Participants with SCC (n=35; 73.9 years-old, SD=9.6, range: 60-95; 62.9% female; 94.3% White) and without SCC (n=33; 71.0 years-old, SD=7.2, range: 61-85, 75.8% female; 100% White) completed a neuropsychological test battery of memory and executive functions, including the Rey Auditory Verbal Learning Test, Trail Making Test Parts A and B, Controlled Oral Word Association Test, Digit Span, and Letter-Number Sequencing, and underwent structural MRI. MR images were analyzed for frontoparietal network volume, thickness, and connectivity.Results:Participants with and without SCC were compared on the number of low test scores (i.e., at or below the 16th percentile) and high test scores (i.e., at or above the 75th percentile), finding a comparable number of low scores, t=1.66, p=.103, d=.40, but a lower number of high scores among participants with SCC, t=2.95, p=.004, d=.71. Participants with SCC had lower bilateral mean frontoparietal network volumes (left: t=2.98, p=.004, d=.74; right: t=2.63, p=.011, d=.66) and cortical thickness (left: t=2.65, p=.010, d=.66; right: t=2.18, p=.033, d=.54), but did not differ from those without SCC in terms of network connectivity.Conclusions:SCC have been reported as a potential risk factor for dementia in older adults. High-functioning older adults with SCC presented with fewer high scores than those without SCC but had a comparable number of low scores. Among high-functioning older adults, subjective cognitive decline may correspond with objective cognitive change not detected by the traditional emphasis on low scores, but rather the absence of high scores. SCC were also related to underlying changes in the volume and thickness of the frontoparietal network, but not connectivity. In high-functioning older adults, subjective cognitive decline may correspond with a reduction from high average functioning in some domains and underlying neurological changes.