Orbitofrontal cortex: neuronal representation of oral temperature and capsaicin in addition to taste and texture.

The primate orbitofrontal cortex is a site of convergence of information from primary taste, olfactory and somatosensory cortical areas. We describe the discovery of a population of single neurons in the macaque orbitofrontal cortex that responds to the temperature of a liquid in the mouth. The temperature stimuli consisted of water at 10 degrees C, 23 degrees C, 37 degrees C and 42 degrees C. Twenty-six of the 1149 neurons analyzed (2.3%) responded to oral temperature. The tuning profiles of the neurons to temperature showed that some of the neurons had graded responses to increasing temperature (27%), others responded to cold (10 degrees C) stimuli (27%), and others were tuned to temperature (46%). The neuronal responses were also measured to taste stimuli, viscosity stimuli (carboxymethyl-cellulose in the range 1-10,000 cP), and capsaicin (10 microM). Of 70 neurons with responses to any of these stimuli, 7.1% were unimodal temperature; 11.3% were temperature and taste-sensitive; 7.1% were temperature and viscosity-sensitive; and 11.3% were temperature, taste and viscosity sensitive. Capsaicin activated 15.7% of the population of responsive neurons tested. These results provide the first evidence of how the temperature of what is in the mouth is represented at the neuronal level in the orbitofrontal cortex and the first evidence for any primate cortical area that in some cases this information converges onto single neurons with inputs produced by other sensory properties of food, including taste and texture. The results provide a basis for understanding how particular combinations of oral temperature, taste, and texture can influence the palatability of foods.