ORBITOFRONTAL CORTEX NEURONS - ROLE IN OLFACTORY AND VISUAL ASSOCIATION LEARNING

1. The orbitofrontal cortex is implicated in the rapid learning of new associations between visual stimuli and primary reinforcers such as t aste. It is also the site of convergence of information from olfactory , gustatory, and visual modalities. To investigate the neuronal mechan isms underlying the formation of odor-taste associations, we made reco rdings from olfactory neurons in the orbitofrontal cortex during the p erformance of an olfactory discrimination task and its reversal in mac aques. 2. It was found that 68% of odor-responsive neurons modified th eir responses after the changes in the taste reward associations of th e odorants. Full reversal of the neuronal responses was seen in 25% of these neurons. Extinction of the differential neuronal responses afte r task reversal was seen in 43% of these neurons. 3. For comparison, v isually responsive orbitofrontal neurons were tested during reversal o f a visual discrimination task. Seventy-one percent of these visual ce lls showed rapid full reversal of the visual stimulus to which they re sponded, when the association of the visual stimulus with taste was re versed in the reversal task. 4. These findings demonstrate that the re sponses of many orbitofrontal cortex olfactory neurons are modified by and depend on the taste with which the odor is associated. 5. This mo dification is likely to be important for setting the motivational valu e of olfactory stimuli for feeding and other rewarded behavior. Howeve r, it is less complete, and much slower, than the modifications found for orbitofrontal visual neurons during visual-taste reversal. This re lative inflexibility of olfactory responses is consistent with the nee d for some stability in odor-taste associations to facilitate the form ation and perception of flavors.