Neuropsychological correlates of cognitive, emotional-affective and auto-activation apathy in Alzheimer's disease

Apathy symptoms include different dimensions: cognitive (C), emotional-affective (E-Aff) and auto-activation; they have been related to dysfunctions of the dorsolateral, orbito-basal prefrontal cortex and the subcortical frontal connections to the basal ganglia, respectively. In Alzheimer's disease (AD), an association has been found between apathy severity and both executive deficits and atrophy of the dorso-lateral prefrontal cortex; however, it is not clear whether these associations concern only the cognitive aspects of apathy. Furthermore, whether there is an association in AD between E-aff apathy and theory of mind (ToM),the cognitive functions subsumed by the orbito-basal prefrontal cortex, has not been investigated. Aim of the study was to investigate the relationship between C, E-Aff and auto-activation apathy and performance on tasks investigating executive and ToM cognitive functions in AD. For this purpose, 20 AD patients with apathy and 20 matched controls were submitted to an executive and ToM neuropsychological assessment. Apathy was assessed with a weekly diary (ApD) created specifically to assist caregivers in quantifying the C, E-Aff and auto-activation symptomatology of apathy. Correlational analyses showed that AD patients' scores on the Modified Card Sorting Test (MCST) and Emotion Attribution tasks were correlated with most ApD scores. However, regression analyses showed that C diary scores were predicted by MCST performance, E-Aff diary scores by performance on the E-Attribution task and ApD scores measuring auto-activation apathy were predicted by both the MCST and the Emotion Attribution scores. These results confirm the co-occurrence of apathy and executive-function deficits in AD and suggest a specific association between AD patients' executive deficits and the cognitive component of apathy. Furthermore, they document, for the first time, an association between poor performance on tests assessing ToM abilities and the emotional-affective component of apathy in AD patients. Finally, these results are in line with the view that auto-activation apathy reflects the sum of emotional and cognitive processing deficits.