Korsakoff's syndrome (KS) is a neuropsychiatric disorder, caused by a vitamin B1 deficiency. Although it is known that patients with KS display diminished theory of mind functioning and frequently exhibit marked antisocial interactions little attention has so far focused on the integrity of moral decision-making abilities, moral reasoning, and empathy. In an experimental cross-sectional design, 20 patients diagnosed with KS, and twenty age-, education-, and gender-equivalent healthy participants performed tests assessing moral decision-making, moral reasoning maturity, empathy, and executive functioning. Participants were administered the Moral Behaviour Inventory (MBI) for everyday moral dilemmas, and ten cartoons of abstract moral dilemmas. Responses were scored according to the Kohlberg stages of moral reasoning. Empathy and executive functioning were assessed with the Interpersonal Reactivity Index (IRI) and the Frontal Assessment Battery (FAB). In contrast to frontal traumatic brain injury patients, KS patients did not display a utilitarian bias, suggesting preserved moral decision-making abilities. Of interest, KS patients had significantly lower levels of moral reasoning maturity on everyday moral dilemmas, and abstract moral dilemmas. In patients, empathy was moderately related to the level of moral maturity on both tasks, while executive functioning was not. In conclusion, KS patients have preserved moral decision-making abilities, but their moral reasoning abilities are poorer in everyday and abstract situations. Lower moral reasoning abilities and lower levels of empathy together may be responsible for adverse social functioning in KS.
