Emotion comprehension in the temporal variant of frontotemporal dementia

Frontotemporal dementia (FTD) is a neurodegenerative disease characterized by behavioural disorders that suggest abnormalities of emotional processing. Patients with the temporal variant of FTD (tvFTD) are particularly at risk for developing deficits in emotional processing secondary to atrophy in the amygdala, anterior temporal cortex (ATC) and orbital frontal cortex (OFC), structures that are components of the brain's emotional processing systems. In addition, previous studies have suggested that predominantly right, as opposed to left temporal atrophy is more likely to be associated with behavioural and emotional impairments in tvFTD. However, emotional processing has never been assessed directly in this group. We examined one aspect of emotional processing, namely the comprehension of facial expressions of emotion (emotional comprehension) in nine individuals with tvFTD, and correlated performance on this measure with atrophy (as measured from T-1-weighted MRI scans by region of interest analysis) in the amygdala, ATC and OFC. Compared with age-matched controls, the tvFTD group was impaired in emotional comprehension, with more severe impairment for emotions with negative valence, including sadness, anger and fear, than for happiness. Emotional comprehension was correlated with atrophy in the right amygdala and the right OFC, and not with atrophy in other structures. When individual profiles of amygdala atrophy were examined across patients and compared with control values, right amygdala atrophy was always accompanied by left amygdala atrophy, whereas patients with volume loss in the left amygdala could have normal or decreased right amygdala volumes. Thus, emotional comprehension appeared to be most impaired when bilateral amygdala atrophy was present, and was not associated with the degree of left amygdala atrophy. Our data indicate that tvFTD is associated with impairments in emotional processing that may underlie some behavioural problems in this disorder, and that the emergence of such deficits depends on the specific pattern of anatomical injury. These results have implications both for the clinical presentation in tvFTD patients and for the study of the neuroanatomical basis of emotion.