Dethier V G, Crnjar R M
J Gen Physiol. 1982 Apr;79(4):549-69. doi: 10.1085/jgp.79.4.549.
Larvae of tobacco hornworms offer unique opportunities to relate the electrophysiological output of identified chemosensory neurons to specific behavioral responses. Larvae can discriminate among three preferred plants with only eight functioning gustatory receptors. They can be induced to prefer any one of the plants, and these preferences can be reversed. All eight neurons respond to each plant sap. Two fire too infrequently to permit detailed analysis. Analyses of the remaining six show that all electrophysiological responses consist of phasic and tonic components. Only the "salt best" cell fires during the phasic period. Temporal analysis of the spike train during this period shows that tomato and tobacco could be distinguished from Jerusalem cherry but not from each other by a rate code. Measurements of behavioral response times together with the nonspecificity of this with respect of food plants, unacceptable plants, and sodium chloride eliminate a phasic period rate code as a probable mechanism for complex discrimination. Events occurring in the tonic period, when all cells are firing, suggest a major role for this period. Analyses of variance in the interval frequencies of the large and medium spikes suggest that a variance code could allow discrimination among the three plants as long as both cells were firing at the same time. Evidence has been found for temporal patterning in the tonic response of the "salt best" cell to Jerusalem cherry but is absent elsewhere. The most likely basis for coding the difference between each of the three plants is across-fiber patterning in which the relative rates of firing and the variances of all the sensory neurons in the tonic phase are critical.
烟草天蛾幼虫为将已识别的化学感应神经元的电生理输出与特定行为反应联系起来提供了独特的机会。幼虫仅用八个起作用的味觉感受器就能区分三种偏好的植物。它们可以被诱导偏好任何一种植物，而且这些偏好可以逆转。所有八个神经元对每种植物汁液都有反应。其中两个神经元放电频率过低，无法进行详细分析。对其余六个神经元的分析表明，所有电生理反应都由相位和紧张性成分组成。只有“对盐反应最佳”的细胞在相位期放电。在此期间对脉冲序列的时间分析表明，番茄和烟草可以通过频率编码与冬珊瑚区分开来，但彼此之间无法区分。行为反应时间的测量以及其对食用植物、不可接受植物和氯化钠的非特异性排除了相位期频率编码作为复杂辨别可能机制的可能性。当所有细胞都在放电时，紧张性期间发生的事件表明该时期起主要作用。对大、中脉冲间隔频率的方差分析表明，只要两个细胞同时放电，方差编码就可以区分这三种植物。已发现“对盐反应最佳”的细胞对冬珊瑚的紧张性反应存在时间模式，但在其他地方不存在。编码这三种植物之间差异的最可能基础是跨纤维模式，其中所有感觉神经元在紧张性阶段的相对放电率和方差至关重要。
