The joint memory effect: challenging the selfish stigma in Huntington's disease?

The prevalent belief that individuals with Huntington's disease exhibit selfish behaviour, disregarding the thoughts, feelings and actions of others, has been challenged by patient organizations and clinical experts. To further investigate this issue and study whether participants with Huntington's disease can pay attention to others, a joint memory task was carried out in patients with Huntington's disease with and without a partner. This study involved 69 participants at an early stage of Huntington's disease and 56 healthy controls from the UK, France and Germany, who participated in the international Repair-HD multicentre study (NCT03119246). Participants completed a semantic categorization task across three categories: animals, fruits and vegetables and manufactured objects. They performed the task either alone (Alone condition) or with the examiner acting as a partner (Pair condition). In the Pair condition, the participant was assigned one category, their partner was assigned another and one category was left unassigned. Afterwards, participants engaged in a surprise free recall task to remember as many words as possible. Words not assigned to anyone were considered socially irrelevant in contrast to the ones assigned to the participant and to the partner. Both groups demonstrated the expected self-prioritization effect, recalling their assigned words better than their partner's or unassigned words in both conditions. Additionally, a joint memory effect was observed, with better recall for the partner's assigned words than the unassigned words in the Pair condition (controls: difference = 0.45, P < 0.001; participants with Huntington's disease: difference = 0.34, P < 0.001). Socially relevant words were thus better recalled than irrelevant words. The number of recalled words correlated with cognitive performance (all P-values < 0.05) and MRI analysis revealed a negative correlation between the joint memory effect and right orbitofrontal grey matter density in participants with Huntington's disease. These findings challenge the notion that individuals with Huntington's disease display selfish behaviours because of disinterest in others. They show the ability to process information about their partners, implying that their social difficulties may arise from factors other than social cognition deficits. This opens the door for more ecological assessments of social cognition in patients with Huntington's disease.