Taste in the Medial Orbitofrontal Cortex of the Macaque

doi:10.1196/annals.1401.007

^{^a} Department of Neural and Behavioral Science, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA ^{^b} Departments of Medicine & Neuroscience, Albert Einstein College of Medicine, Bronx, New York 10461, USA ^{^c} Office of Graduate and Research Affairs, San Diego State University, San Diego, California 92182, USA

Taste activates about 6% of the neurons in the anterior insula(primary taste cortex) of the macaque. The anterior insula hasmany direct and indirect projections to the orbitofrontal cortex(OFC), including the caudolateral OFC (clOFC), where only 2%of the neurons respond to taste. We have identified a 12-mm²region in the medial OFC (mOFC) where taste represents 7–28%of the population. This rich trove of taste cells has functionalcharacteristics typical of both the insular cortex that projectsto it and the clOFC to which it projects. Mean spontaneous ratewas 3.1 spikes/s, nearly identical to that in the insula, butdouble that of the clOFC. In the mOFC, 19% of the taste cellsalso responded to other modalities, most commonly olfactionand touch, slightly less than the 27% in the clOFC. The distributionof best stimulus neurons was almost even across the four prototypicalstimuli in the mOFC, as in insula, but discrepant from the clOFC,where sugar responsiveness dominated. The broadly tuned tasteneurons in the mOFC were similar to those in the insula andstrikingly different from the more specialized cells of theclOFC. Whereas the responsiveness to the taste of a satiatingstimulus declines among the narrowly tuned clOFC cells, satietyhas much less impact on the responsiveness of mOFC neurons.The mOFC is a robust area worthy of exploration for its involvementin gustatory coding, the amalgamation of sensory inputs to createflavor, and the hedonics that guide feeding.

Part II. The Orbitofrontal Cortex and Chemosensory Function