Electrophysiological and behavioral evidences of the feeding-related neuronal processes in the orbitofrontal cortex

The orbitofrontal cortex (OBF) is known to play an important role in the central regulation of adaptive behavior. Previous studies provided evidence for feeding-associated neurons in the rodent and macaque OBF. To further elucidate functional attributes of these neurons, complex electrophysiological–neurochemical–behavioral studies were performed in rats and rhesus monkeys. Single unit activity was recorded in the rat and monkey OBF during microiontophoresis of glucose, various neurochemicals, as well as gustatory stimulations. To investigate feeding-related neuronal mechanisms at the cognitive level, recordings were also performed in the monkey OBF during a visual food discrimination task. OBF neurons displayed specific responsiveness to gustatory stimuli, as well as to microelectrophoretically applied chemicals. The majority of gustatory cells were shown to possess specific, feeding-related neurochemical attributes: microelectrophoretically administered glucose changed their firing rates. These chemosensory cells also displayed differential sensitivity to catecholamines and other neurochemicals. In the discrimination task, category-specific or task-specific neurons showed a broad variety of selectivity for food-related visual stimuli. Expectation- and reward-related activities were also recorded. Our results provide evidence that OBF neurons possess specific endogenous and exogenous chemosensitivity, and that they utilize differential neurotransmitter mechanisms in feeding-related cognitive functions. Thus, the complex network of these chemosensory neurons possesses broad ranging, multiple functional attributes in the homeostatic control.