Background Apathy is a reduction in goal directed behaviour. It is one of the commonest neuropsychiatric features of Huntington’s disease (HD), causing impairments in quality of life and function. Our understanding of the neuropsychological basis of apathy in HD is very limited; developing a battery of objective tests would overcome the limitations of current questionnaire-based tests (limited translational potential and distortion by social context) and allow us to determine the underlying deficits of the apathy syndrome in HD.
Aims To develop a battery of tests assessing different aspects of apathy, in order to probe the specific deficits underlying apathy in Huntington’s disease.
Methods A cohort of participants carrying the gene expansion for HD, at various stages of the illness, from asymptomatic to moderate stages of the motor symptomatic phase of HD was recruited. We used the current gold standard assessments (PBA Apathy Score and Apathy Evaluation Scale) and compared them with tests of reward (a novel reaction time task, reward responsiveness subscale of the BISBAS), effort (Progressive Ratio), sensitivity to negative stimuli (a novel persistence task), decision-making (a novel decision-making task) and learning (Iowa Gambling Task and Probabilistic Selection Learning Task).
Results Fifty-three gene positive individuals were recruited. Using linear regression analyses corrected for age, disease and drug effects we found that both apathy measures were related to impaired sensitivity to negative stimuli and deficits in decision making, but not to measures of effort, reward or learning.
Conclusions Patients’ apathy is not related to reward or effort, but inertia due to impaired ability to formulate and enact a plan to change current behaviour. Prompting may be the most effective behavioural intervention.