Symptoms of frontotemporal dementia provide insights into orbitofrontal cortex function and social behavior

Recent investigations into the brain substrates of behavioral changes in frontotemporal dementia (FTD) demonstrate that the orbitofrontal cortex (OFC) plays a crucial role in normal social and emotional behavior. The initial symptoms of FTD reflect the early involvement of OFC as well as the disruption of an associated network involving the insula, striatum, and medial frontal lobes. As predicted by patients with other types of OFC lesions, FTD patients show impairments involving stimulus-reward reversal learning, response inhibition, and ability to judge the appropriateness of their behavior in the social context. While the natural reward system remains intact in these patients, that is, patients will seek out directly rewarding stimuli, such as food and sex, with progressive OFC dysfunction they lose the ability to process complex stimulus-reward contingencies. These abnormalities are apparent in their social interactions, which break down early in the disease. Also, deficits in emotion recognition and empathy have been directly linked to OFC atrophy in these patients. In contrast, some patients with early FTD show intact cognitive skills, including memory and executive functioning. Here, we review the behavioral and neuropsychological changes that accompany OFC atrophy in FTD and argue that phylogenetically new neurons found in this region, called von Economo neurons, are selectively vulnerable in FTD.