After repetitious sucrose stimulation saltiness suppression in NaClsucrose mixtures is diminished: implications for a central mixture suppression mechanism

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Abstract
Human subjects estimated the saltiness of sequences of taste stimuli by a modified magnitude-estimation procedure. The last stimulus in a sequence was always a NaCl/sucrose mixture, whereas the preceding stimuli were a number of sucrose stimuli. Sensory adaptation was prevented by choosing short stimulus durations and long inter-stimulus intervals and by mouth-rinsing between stimuli. Saltiness suppression in the mixture was diminished in a logarithmic-like way by habituation to NaCl and this effect became more pronounced with increasing numbers of preceding sucrose stimuli. The steepness of the saltiness-recovery function depends upon the amount of mixture suppression and all functions converge at a point where mixture suppression is about zero. On the basis of these and previous results it is hypothesized that NaCl/sucrose mixtures excite two independent neuronal taste centers which have inhibitory projections to each other. Furthermore, the results suggest a functional distinction between neural activity leading to intensity sensation and neural activity associated with mixture suppression.