ABSTRACT
The brain areas that represent taste also provide a representation of oral texture. Fat texture is represented by neurons independently of viscosity: some neurons respond to fat independently of viscosity, and other neurons encode viscosity. The neurons that respond to fat also respond to silicone oil and paraf n oil, indicating that the sensing is not chemospeci c, but is instead based on texture. This fat sensing is not related to free fatty acids (FFA), in that these neurons typically do not respond to FFA such as linoleic acid (LiA). Moreover, a few neurons with responses to FFA typically do not respond to fat in the mouth. Fat texture-sensitive neurons are found in the primary taste cortex in the rostral insula and adjoining frontal operculum, in the secondary taste cortex in the orbitofrontal cortex, and in the amygdala. In these regions, the fat texture responsiveness of these neurons may be combined with taste and/or oral temperature responses, and in the orbitofrontal cortex with olfactory responses. Different neurons respond to different combinations, providing a rich representation of the sensory properties of food. In the orbitofrontal cortex, feeding to satiety with one food decreases the responses of these neurons to that food, but not to other foods, showing that sensory-speci c satiety and appetite modulation are represented in the orbitofrontal cortex. A complementary functional neuroimaging study in humans showed activation by fat in the mouth of the insula, orbitofrontal cortex, and a region to which it projects, the pregenual cingulate cortex. In summary, one way in which fat in the mouth is represented in the brain is by its texture, and an indication of what must be transduced has been provided by these neuroscience studies.
