Putting things into perspective: the nature and impact of theory of mind impairment in Huntington's disease.

In Huntington's disease (HD), frontostriatal dysfunction may lead to deficits in theory of mind (ToM), in addition to broader cognitive impairment. We investigated relationships between patients' spatial and social perspective taking performance and executive deficits, self-reported everyday perspective taking, motor symptoms, functional capacity and quality of life. Thirty patients with symptomatic HD and twenty-three healthy controls of similar age and education completed two ToM tasks, a scale assessing everyday interpersonal perspective taking, a novel object-based spatial perspective taking task (SPT) and executive measures. Ratings of quality of life, psychiatric symptoms, motor symptom severity and functional capacity were also taken for patients. When compared to controls, patients exhibited significant deficits in ToM and spatial perspective taking and lower everyday perspective taking scores. Executive deficits were linked to poor understanding of socially inappropriate remarks and errors in mental state attribution. This may be the first study to show that aspects of ToM performance are linked to spatial perspective taking, motor symptom severity and functional capacity in HD. Our findings indicate that patients with HD exhibit evidence of reduced perspective taking in everyday life in addition to poor performance on social and SPTs. They also emphasise the need to better specify the precise cognitive and neural bases for ToM deficits in neurodegenerative conditions. Further research exploring the impact of striatal degeneration on perspective taking abilities will make a valuable contribution to the continued development of functional models of frontostriatal circuitry.