OLFACTORY NEURONAL RESPONSES IN THE PRIMATE ORBITOFRONTAL CORTEX - ANALYSIS IN AN OLFACTORY DISCRIMINATION TASK

1. The primate orbitofrontal cortex receives inputs from the primary o lfactory (pyriform) cortex and also from the primary taste cortex. To investigate how olfactory information is encoded in the orbitofrontal cortex, the responses of single neurons in the orbitofrontal cortex an d surrounding areas were recorded during the performance of an olfacto ry discrimination task. In the task, the delivery of one of eight diff erent odors indicated that the monkey could lick to obtain a taste of sucrose. If one of two other odors was delivered from the olfactometer , the monkey had to refrain from licking, otherwise he received a tast e of saline. 2. Of the 1,580 neurons recorded in the orbitofrontal cor tex, 3.1% (48) had olfactory responses and 34 (2.2%) responded differe ntly to the different odors in the task. The neurons responded with a typical latency of 180 ms from the onset of odorant delivery. 3. Of th e olfactory neurons with differential responses in the task, 35% respo nded solely on the basis of the taste reward association of the odoran ts. Such neurons responded either to all the rewarded stimuli, and non e of the saline-associated stimuli, or vice versa. 4. The remaining 65 % of these neurons showed differential selectivity for the stimuli bas ed on the odor quality and not on the taste reward association of the odor. 5. The findings show that the olfactory representation within th e orbitofrontal cortex reflects for some neurons (65%) which odor is p resent independently of its association with taste reward, and that fo r other neurons (35%), the olfactory response reflects (and encodes) t he taste association of the odor. The additional finding that some of the odor-responsive neurons were also responsive to taste stimuli supp orts the hypothesis that odor-taste association learning at the level of single neurons in the orbitofrontal cortex enables such cells to sh ow olfactory responses that reflect the taste association of the odor.