The Neural Basis of Disorders of Social Knowledge: Major Depressive Disorder and Frontotemporal Dementia

Abstract

A fronto-temporo-mesolimbic integration model of moral cognition proposed that the experience of self- and other-blaming feelings is dependent upon integration of different forms of representations including: 1) differentiated conceptual representations about social behaviours served by the anterior temporal lobe, 2) sequential representations about the consequences of social actions in the ventral frontal lobes, and 3) motivational state representations in mesolimbic regions. Here, I use this model to investigate overgeneral forms of self-blaming feelings, such as self-contempt in remitted Major Depressive Disorder (MDD), and inappropriate social behaviour of patients with Frontotemporal Lobar Degeneration (FTLD). Individuals with remitted MDD demonstrated an increased proneness to experience overgeneral self-blaming feelings (self-contempt bias). This was associated with decreased conceptual differentiation when evaluating one's own social behaviour relative to that of others, combined with the tendency to find one's own behaviours more unpleasant than that of other people. An fMRI study revealed that compared to a control group, people with remitted MDD exhibited decreased functional connectivity across a fronto-temporo-limbic network that was selective for self-blaming relative to other-blaming feelings. These findings provide a neural mechanism for self-blaming biases, thereby helping to understand vulnerability to MDD. In the FTLD study, we demonstrated a double dissociation between deficits in conceptual and sequential social knowledge in patients with Semantic (SD) and Frontotemporal Dementia (FTD) respectively. This could partly explain the inappropriate social behaviours occurring in both of these groups. These results shed new light on the basis of self-blaming biases in MDD and inappropriate social behaviour in FTLD, and provide a platform for future investigations of these disorders from this perspective.

Date of Award	31 Dec 2011
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Matthew Lambon Ralph (Supervisor) & Roland Zahn (Supervisor)