Taste neurons in the cortex of the alert cynomolgus monkey.

The activity of single neurons in the gustatory cortex of alert cynomolgus monkeys was analyzed. Taste-evoked activity in response to the four prototypical taste stimuli was recorded from a cortical gustatory area comprising the frontal operculum and adjoining anterior insula. Spontaneous activity for 364 gustatory neurons was 3.9 +/- 4.9 (mean +/- SD) spikes/s. Mean net (gross minus spontaneous) discharge rates for all gustatory neurons were: 1.0 M glucose = 4.9 +/- 11.6, 0.3 M NaCl = 3.2 +/- 7.1, M quinine HCl = 2.6 +/- 5.8, and 0.01 M HCl = 1.7 +/- 4.6. The results from intensity-response functions imply that the perception of each basic taste quality in the nonhuman primate is based on the activity of the appropriate neural subgroup rather than on the mean activity of all taste cells. Therefore a more meaningful index of the effectiveness of a stimulus may be the discharge rate it evokes from the subset of gustatory neurons for which it is the best stimulus. Glucose was the best stimulus for 142 cells (including ties), from which it elicited a mean net response of 10.3 spikes/s; NaCl was best for 107 neurons which gave a mean 8.7 spikes/s; quinine HCl evoked 6.2 spikes/s from the 74 cells that responded best to it; HCl elicited 5.9 spikes/s from the 49 neurons for which it served as best stimulus. The response characteristics of cortical taste cells indicate heterogeneous features, and significantly different patterns from those reported in other nonchemical sensory systems.