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  3. It may be debated whether individual neurons are "tuned" to react to only a single tastant such as salt or sugar-and ther

It may be debated whether individual neurons are "tuned" to react to only a single tastant such as salt or sugar-and ther

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问题             It may be debated whether individual neurons are "tuned" to react to only a
       single tastant such as salt or sugar-and therefore signal only one taste
       quality-or whether the activity in a given neuron contributes to the neural
Line    representation of more than one taste. Studies show that both peripheral and
(5)     central gustatory neurons typically respond to more than one kind of stimulus,
       and although each neuron is attuned most acutely to one tastant, it usually also
       generates a reaction to others with dissimilar taste qualities. How then can the
       brain represent various taste qualities if each neuron is receptive to many
       different-tasting stimuli?
(10)         Electrophysiological studies of gustatory sensory neurons, first performed
       by Pfaffmann, demonstrated that peripheral neurons are not specifically
       responsive to stimuli representing a single taste quality (which might be
       symbolized by the pattern of activity across gustatory neurons because the
       activity of any one cell was ambiguous) but instead record a spectrum of tastes.
(15)    But in the 1970s and 1980s several scientists began to accumulate data indicating
       that individual neurons are tuned maximally for one taste, and they interpreted
       this as evidence that activity in a particular type of cell represented a given taste
       quality—an idea they called the labeled-line hypothesis. According to this idea,
       activity in neurons that experience the strongest reaction to sugar would signal
(20)    "sweetness," activity in those that are most sensitive to acids would signal
       "sourness", and so forth.
           Smith later proved that the same cells that previous researchers had
       interpreted as labeled lines actually defined the similarities and differences in
       the patterns of activity across taste neurons, suggesting that the same neurons
(25)    were responsible for taste-quality representation, whether they were viewed as
       labeled lines or as critical parts of an across-neuron pattern. These investigators
       further established that the neural distinction among stimuli of different
       qualities depended on the simultaneous activation of different cell types, much
       as with the function of color vision, but unlike auditory perception. These and
(30)    other considerations have led us to favor the idea that the patterns of activity
       are key to coding taste information.
           Scientists now know that things that taste similarly evoke similar patterns
       of activity across groups of taste neurons. Furthermore, we can compare these
       patterns and use multivariate statistical analysis to plot the similarities in the
(35)    patterns elicited by various tastants. Taste researchers have generated such
       comparisons for gustatory stimuli from the neural responses of hamsters and
       rats and these correspond very closely to similar plots generated in behavioral
       experiments, from which we may infer which stimuli taste alike and which taste
       different to animals. Such data show that the across-neuron patterns contain
(40)    sufficient information for taste discrimination and this may be a reasonable
       explanation for neural coding in taste, though researchers continue to debate
       whether individual neuron types play a more significant role in taste coding than
       they do in color vision. Scientists question whether taste is an analytic sense, in
       which each quality is separate, or a synthetic sense like color vision, where
(45)    combinations of colors produce a unique quality.
According to the passage, Pfaffman’s theory differs from that which has been most recently considered by scientists in that it
选项 A、postulates that peripheral neurons do not respond to a greater extent to stimuli representing a single taste quality
B、ignores the crucial difference between central and peripheral gustatory neurons in their role as mechanisms of taste
C、implies that the activity of any individual taste cell, taken by itself, is ambiguous
D、fails to acknowledge that specific gustatory neurons are associated with particular tastes
E、relies primarily upon research data that has come from human, rather than animal, subjects
答案D
解析
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