Social Cognition and Functioning in Huntington’s Disease

Abstract

Huntington's Disease (HD) is a neurodegenerative disease caused by an expansion mutation in the huntingtin gene. Although it is classified as a movement disorder, other prominent features include early cognitive, behavioural and neuropsychiatric symptoms. These non-motor features have a greater impact on quality of life than motor-related ones. Specifically, problems with social functioning are often reported as one of the most difficult to manage symptoms by patients and their companions. While problems in certain areas of social cognition are well-established, there is little understanding of how specific cognitive deficits translate to functional impairment. This thesis aims to explore how cognitive and neuropsychiatric deficits relate to problems of social functioning. I first assessed performance across a wide range of cognitive domains thought to be related to social functioning and previously found to be impaired in early HD. These included social cognition, decision-making, executive function, reinforcement learning and neuropsychiatric problems. In line with the existing literature, I found reduced performance in the domains of social cognition and executive function at early manifest stages of the disease. Furthermore, I showed that executive function appears to be an impairment independent of other cognitive problems. However, some specific social cognitive deficits are predicted by motivational processes, suggesting that reduced motivation to attend to social stimuli might lead to reduced social cognition. Next, I assessed social functioning through self and proxy-rated questionnaires, computerised tasks and an assessment of loneliness. This was then connected to potential underlying cognitive and neuropsychiatric factors, discussed in the previous paragraph. Results showed that social functioning problems are primarily reported by companions of HD manifest individuals. Furthermore, a deficit in detecting lies was found specifically for situations where controls can use social understanding to improve their performance. Only neuropsychiatric problems and motor problems significantly predicted performance on self-reported social function measures for manifest participants. The final project focused on loneliness and social isolation in HD and Parkinson’s Disease (PD). While both diseases are related to reduced social functioning at early stages, little is known about how those social functioning problems relate to loneliness and social isolation. Results showed that HD manifest participants are more likely to be socially isolated without experiencing loneliness than controls. This profile was primarily predicted by social anhedonia scores. In comparison, PD participants were more likely to be both socially isolated and lonely, which was predicted by self-rated social function. Compared to each other, the two disease groups differed significantly in terms of more HD manifest participants classifying as socially isolated and more PD patients as lonely. Hence, the specific profiles of loneliness and social isolation and their underlying factors are disease dependent. In summary, I aimed to bridge the gap between specific cognitive problems and difficulties in social functioning and then relate this to potential negative outcomes such as loneliness and social isolation.