Gustatory responses in the frontal opercular cortex of the alert cynomolgus monkey

Abstract

SUMMARYAND CONCLUSIONS1. The responses of 165 single taste neurons in the anterior operculum of the alert cynomolgus monkey were analyzed. Chemicals were deionized water, blackcurrant juice, and the four basic taste stimuli: glucose, NaCl, HCl, and quinine HCl.2. Taste-evoked responses could be recorded from an opercular region that measured -4.0 mm in its anteroposterior extent, 2.0 mm mediolaterally, and 3.0 mm dorsoventrally. Within this area, taste-responsive neurons were sparsely distributed such that multiunit activity was rarely encountered and neuronal isolation was readily achieved.3. Intensity-response functions were determined for nine cells. In each case, the lowest concentration of the dynamic response range conformed well to human electrophysiological and psychophysical thresholds for the basic taste stimuli.4. There was some evidence of chemotopic organization. Cells that responded best to glucose tended to be distributed toward the anterior operculum, whereas most acid-sensitive neurons were located more posteriorly. The proportion of cells responding best to NaCl peaked in the middle of the area, whereas quinine sensitivity was rather evenly distributed throughout.5. Opercular neurons in the monkey showed moderate breadth of sensitivity compared with taste cells of other species and at other synaptic levels. A breadth-of-tuning coefficient was calculated for each neuron. This is a metric that can range from 0.0 for a cell that responds specifically to only one of the four basic stimuli to 1.0 for one that responds equally to all four stimuli. The mean coefficient for 165 cells in the operculum was 0.67 (range = 0.12-0.99).6. Efforts were made to determine whether neurons could be divided into a discrete number of types, as defined by their responsiveness to the stimulus array used here. It was concluded that most taste cells may be assigned to a small number of groups, each of which is statistically independent of the others, but within which the constituent neurons are not identical.7. An analysis of taste quality indicated that the sweet and salty stimuli evoked patterns of activity that were significantly intercorrelated. Similarly, patterns representing HCl, quinine HCl, and water were related.

Neurobiology of anorexia and bulimia nervosa

“…That is, a primary taste cortex resides in the rostral insula and adjoining frontal operculum (189)(190)(191)(192). Some studies argue that these regions provide a representation of food in the mouth that is independent of hunger, and thus is of reward value (193).…”

Taste, olfactory and food texture reward processing in the brain and obesity

“…The primary taste cortex Rolls et al [2][3][4] have shown that the primary taste cortex in the primate anterior insula and adjoining frontal operculum contains not only taste neurons tuned to sweet, salt, bitter, sour, and umami as exemplified by monosodium glutamate (MSG), 5,6 but also other neurons that encode oral somatosensory stimuli including viscosity, fat texture, temperature and capsaicin. 7 Some neurons in the primary taste cortex respond to particular combinations of taste and oral texture stimuli, but do not respond to olfactory stimuli or visual stimuli such as the sight of food.…”

Altered Insula Response to Taste Stimuli in Individuals Recovered from Restricting-Type Anorexia Nervosa

“…Brain imaging studies performed in the past decade in human and nonhuman primates show that a primary taste cortex resides in the rostral insula and adjoining frontal operculum (Scott et al, 1986;Yaxley et al, 1990;Faurion et al, 1999;Schoenfeld et al, 2004). Some studies argue that these regions provide a representation of food in the mouth that is independent of hunger, and thus of reward value (Rolls, 2005).…”

“…This concentration is present in soft drinks and is a level of sweetness preferred by the general public (Drewnowski et al, 1987;Sunday and Halmi, 1990). In primates and healthy humans, both sugar (Rolls, 2005) and water (Scott et al, 1986;Yaxley et al, 1990;Zald and Pardo, 2000;De Araujo et al, 2003a) ingestion activates neurons in the primary and secondary cortical taste areas. We hypothesize that AN women might have a disturbance of these higher order pathways modulating the sensory and hedonic aspects of feeding.…”