Taste in the medial orbitofrontal cortex of the macaque.

Taste activates about 6% of the neurons in the anterior insula (primary taste cortex) of the macaque. The anterior insula has many 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-mm(2) region in the medial OFC (mOFC) where taste represents 7-28% of the population. This rich trove of taste cells has functional characteristics typical of both the insular cortex that projects to it and the clOFC to which it projects. Mean spontaneous rate was 3.1 spikes/s, nearly identical to that in the insula, but double that of the clOFC. In the mOFC, 19% of the taste cells also responded to other modalities, most commonly olfaction and touch, slightly less than the 27% in the clOFC. The distribution of best stimulus neurons was almost even across the four prototypical stimuli in the mOFC, as in insula, but discrepant from the clOFC, where sugar responsiveness dominated. The broadly tuned taste neurons in the mOFC were similar to those in the insula and strikingly different from the more specialized cells of the clOFC. Whereas the responsiveness to the taste of a satiating stimulus declines among the narrowly tuned clOFC cells, satiety has much less impact on the responsiveness of mOFC neurons. The mOFC is a robust area worthy of exploration for its involvement in gustatory coding, the amalgamation of sensory inputs to create flavor, and the hedonics that guide feeding.