Gustatory cortex of primates: anatomy and physiology

Clinical and physiological studies of patients with ageusia or gustatory hallucination suggest that the primary gustatory area (area G) lies at the anterior insula or at the base of the central sulcus. However, physiological and anatomical studies in subhuman primates, e.g. squirrel monkeys or macaque monkeys, locate area G at the buried frontal operculum (Fop) and dorsal insula. The presence of secondary or higher gustatory areas are claimed because taste neurons are found in the precentral opercular area (PrCO) or orbitofrontal cortex in alert monkeys. Part of the anterior insula is suggested to subserve the interface between area G and the amygdala. Many physiological studies have been conducted lacking knowledge of the histological boundaries of the primary and secondary gustatory areas. Some difference has been found in the physiological properties of taste neurons in the primary and secondary gustatory areas: the primary gustatory area contains various categories of taste neurons, whereas most of the taste neurons in the secondary gustatory areas (e.g., PrCO, area 1-2) are specifically sensitive to one of the four basic tastes, and taste neurons in the orbitofrontal opercular area (OFO), another secondary gustatory area, show sensory-specific hunger as well.