The neurocognitive correlates of loneliness in older adults

Abstract

Loneliness is defined as the subjective feeling of being socially isolated, resulting in a disparity between an individual’s social needs and social experiences in real life It is considered to have both affective and cognitive implications and is one of the major risk factors for both physical and psychological malfunctioning. On the affective side, loneliness is related to depression, especially in older population and is typically associated with higher levels of anxiety, negative mood, and depressive symptomology. On the cognitive side, perceived loneliness is thought to have increased risk for Alzheimer’s disease, cognitive decline over time and dysfunction in cognitive performance, and decline in executive control. This thesis systematically investigates the association between perceived loneliness, executive control functioning and brain structure in both clinical (late-life depression) and normative samples. Study one was conducted in a group of older adults suffering from late-life depression. Results showed higher loneliness level in the group of depressed patients with more relapses, and loneliness was also associated with reduced grey matter volume in the striatum in this group of subjects. These findings suggest that loneliness may contribute to depression in older age groups by interfering with how the brain processes stimuli with affective values. The second study investigated the relationship between perceived loneliness and executive control processes in a large normative sample of older adults. A battery of neurocognitive tests was done in older adults to investigate whether loneliness could be independently predicted by cognitive domains, such as planning, working memory, attention control and response inhibition, and depressive characteristics while controlling for other demographic information. The performance on the Tower of London task, which assesses planning and working memory, significantly predict perceived loneliness even after accounting for depressive features assessed by the Geriatric Depression Scale. This finding suggests planning and working memory functions is an important predictor of loneliness level in older adults, which is also related to greater risk for major depression. The final study further investigated the neural structural mechanisms that may underlie the relationship between loneliness and executive control functioning in older adults. Findings showed that perceived loneliness and the executive control functioning components found in study two shared common neural correlates, namely the dorsomedial prefrontal cortex and the supplementary motor area. It was further found that the grey matter volume of these two regions mediated the relationship between loneliness and executive control functioning in the group of older adults. The results from the three studies collectively delineate the brain structural correlates of loneliness in both clinical and normative older people. These brain correlates could help with early identification of older individuals who might be vulnerable for developing mood disorders due to a lack of social support and serve as an objective index for evaluating the effectiveness of therapeutic efforts to improve cognitive and emotional health in the older population. A pathway model was developed to focus on the role of loneliness in older adults who develop late-life depression based on the results of the 3 studies.