Flavour processing in semantic dementia

The cognitive mechanisms for the analysis of flavour information remain poorly understood. Patients with semantic dementia (SD) could potentially provide a window on these mechanisms; however, while abnormal eating behaviour and altered food preferences are common in SD, flavour processing has been little studied in this disorder. Here we undertook a detailed investigation of flavour processing in three patients at different stages of SD. One patient with a clinical syndrome of logopenic aphasia (LPA) was studied as a disease control, and six healthy control subjects also participated. Olfaction was assessed using the University of Pennsylvania Smell Identification Test and processing of flavours was assessed using a novel battery to assess flavour perception, flavour identification, and congruence and affective valence of flavour combinations. Patients with SD performed equivalently to healthy controls on the perceptual subtest, while their ability to identify flavours or to determine congruence of flavour combinations was impaired. Classification of flavours according to affective valence was comparable to healthy controls. In contrast, the patient with LPA exhibited a perceptual deficit with relatively preserved identification of flavours, but impaired ability to determine flavour congruence, which did not benefit from affective valence. Olfactory and flavour identification performance was correlated in both patients and controls. We propose that SD produces a true deficit of flavour knowledge (an associative agnosia), while other peri-Sylvian pathologies may lead to deficient flavour perception. Our findings are consistent with emerging evidence from healthy subjects for a cortical hierarchy for processing flavour information, instantiated in a brain network that includes the insula, anterior temporal lobes and orbitofrontal cortex. The findings suggest a potential mechanism for the development of food fads and other abnormal eating behaviours.