Rolls E T, Critchley H D, Browning A, Hernadi I
Department of Experimental Psychology, University of Oxford, England.
Ann N Y Acad Sci. 1998 Nov 30;855:426-37. doi: 10.1111/j.1749-6632.1998.tb10602.x.
To investigate the neural encoding of glutamate (umami) taste in the primate, recordings were made from taste responsive neurons in the cortical taste areas in macaques. Most of the neurons were in the orbitofrontal cortex (secondary) taste area. First, it was shown that there is a representation of the taste of glutamate which is separate from the representation of the other prototypical tastants sweet (glucose), salt (NaCl), bitter (quinine) and sour (HCl). Second, it was shown that single neurons that had their best responses to sodium glutamate also had good responses to glutamic acid. Third, it was shown that the responses of these neurons to the nucleotide umami tastant inosine 5'-monophosphate were more correlated with their responses to monosodium glutamate than to any prototypical tastant. Fourth, concentration response curves showed that concentrations of monosodium glutamate as low as 0.001 M were just above threshold for some of these neurons. Fifth, some neurons in the orbitofrontal region, which responded to monosodium glutamate and other food tastes, decreased their responses after feeding with monosodium glutamate to behavioral satiety, revealing a mechanism of satiety. In some cases this reduction was sensory-specific. Sixth, it was shown in psychophysical experiments in humans that the flavor of umami is strongest with a combination of corresponding taste and olfactory stimuli (e.g., monosodium glutamate and garlic odor). The hypothesis is proposed that part of the way in which glutamate works as a flavor enhancer is by acting in combination with corresponding food odors. The appropriate associations between the odor and the glutamate taste may be learned at least in part by olfactory to taste association learning in the primate orbitofrontal cortex.
为了研究灵长类动物中谷氨酸（鲜味）味觉的神经编码，研究人员对猕猴大脑皮层味觉区域中对味觉有反应的神经元进行了记录。大多数神经元位于眶额皮质（次级）味觉区域。首先，研究表明谷氨酸味觉的表征与其他典型味觉物质（甜味——葡萄糖、咸味——氯化钠、苦味——奎宁、酸味——盐酸）的表征是分开的。其次，研究表明对谷氨酸钠反应最佳的单个神经元对谷氨酸也有良好反应。第三，研究表明这些神经元对核苷酸鲜味剂5'-肌苷酸的反应与其对谷氨酸钠的反应的相关性，比与任何典型味觉物质的反应的相关性都更高。第四，浓度反应曲线表明，对于其中一些神经元而言，低至0.001 M的谷氨酸钠浓度刚好高于阈值。第五，眶额区域中一些对谷氨酸钠和其他食物味道有反应的神经元，在喂食谷氨酸钠至行为饱腹感后，其反应会降低，这揭示了一种饱腹感机制。在某些情况下，这种降低是感官特异性的。第六，在人类的心理物理学实验中表明，鲜味在相应的味觉和嗅觉刺激（例如谷氨酸钠和大蒜气味）相结合时最为强烈。有人提出这样的假说：谷氨酸作为风味增强剂起作用的部分方式是与相应的食物气味结合发挥作用。气味与谷氨酸味觉之间的适当关联可能至少部分是通过灵长类动物眶额皮质中的嗅觉到味觉的关联学习习得的。
