HUNGER AND SATIETY MODIFY THE RESPONSES OF OLFACTORY AND VISUAL NEURONS IN THE PRIMATE ORBITOFRONTAL CORTEX

1. The primate orbitofrontal cortex is the site of convergence of info rmation from primary taste and primary olfactory cortical regions. In addition, it receives projections from temporal lobe visual areas conc erned with the representation of objects such as foods. Previous work has shown that the responses of gustatory neurons in the secondary tas te area within the orbitofrontal cortex are modulated by hunger and sa tiety, in that they stop responding to the taste of a food on which an animal has been fed to behavioral satiation, yet may continue to resp ond to the taste of other foods. 2. This study demonstrates a similar modulation of the responses of olfactory and visual orbitofrontal cort ex neurons after feeding to satiety. Seven of nine olfactory neurons t hat were responsive to the odors of foods, such as blackcurrant juice, were found to decrease their responses to the odor of the satiating f ood in a selective and statistically significant manner. 3. It also wa s found for eight of nine neurons that had selective responses to the sight of food, that they demonstrated a sensory-specific reduction in their visual responses to foods after satiation. 4. The responses of o rbitofrontal cortex neurons selective for foods in more than one modal ity also were analyzed before and after feeding to satiation. Satiety often affected the responses of these multimodal neurons across all mo dalities, but a sensory-specific effect was not always demonstrable fo r both modalities. 5. These findings show that the olfactory and visua l representations of food, as well as the taste representation of food , in the primate orbitofrontal cortex are modulated by hunger. Usually a component related to sensory-specific satiety can be demonstrated. The findings Link at least part of the processing of olfactory and vis ual information in this brain region to the control of feeding-related behavior.