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Abstract: The relationship between neuronal activity in the human gustatory cortex and the concentrations of taste stimuli is not well understood. In this study, we recorded changes in the magnetic fields of the human brain in response to four concentrations of NaCl (30 mM, 100 mM, 300 mM, and 1 M) and measured the magnitude and shortest latency of the equivalent current dipole (ECD) in the primary gustatory area of the cerebral cortex (PGA). The average magnitude of ECDs in the PGA increased in a concentration-dependent manner throughout the entire range of NaCl concentrations. The shortest latency of the ECD, however, did not vary with the stimulus concentration.

Abstract: The relationship between neuronal activity in the human gustatory cortex and the concentrations of taste stimuli is not well understood. In this study, we recorded changes in the magnetic fields of the human brain in response to four concentrations of NaCl (30 mM, 100 mM, 300 mM, and 1 M) and measured the magnitude and shortest latency of the equivalent current dipole (ECD) in the primary gustatory area of the cerebral cortex (PGA). The average magnitude of ECDs in the PGA increased in a concentration-dependent manner throughout the entire range of NaCl concentrations. The shortest latency of the ECD, however, did not vary with the stimulus concentration.

When taste stimuli are presented with specific odor stimuli, the perceived intensity of taste is enhanced, a phenomenon called odor-induced taste enhancement. There is a possibility, however, that the odor substances might have stimulated the taste receptors in the oral cavity as well as odor receptors in the nasal cavity because the odor substances were dissolved in the taste solutions in some preceding studies. Schifferstein and Verlegh (1996) found that the odor-induced taste enhancement effect was not found when the subjects wore a nose clip to prevent the olfactory perception. Thus, it was suggested that the odor-induced taste enhancement did not result from the stimulation of receptors in the oral cavity. To confirm and extend their study, we presented the odor stimuli simultaneously with, but not dissolved in, the taste stimuli with a more advanced approach to stimulus presentation. The participants reported enhancement of sweetness ratings for aspartame when the taste stimuli were presented with a vanilla odor. This odor-induced taste enhancement was found when the gaseous odor stimuli were presented either by the retronasal route or by the orthonasal route. There was little possibility that the vanilla odor stimulated the taste receptors during the orthonasal stimulation because the odor stimuli were presented directly into the nasal cavity. Thus, we could show that the odor-induced taste enhancement is elicited by olfactory perception. These results also suggested that there is little functional difference between retronasal and orthonasal olfaction.