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 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