Regional taste sensitivity to NaCl: relationship to subject age, tongue locus and area of stimulation.

Using a signal detection procedure and a microprocessor-controlled gustometer, sensitivity to three concentrations of NaCl (0.01, 0.1 and 1.0 M) was measured on the tongue tip, and on a region 3.0 cm posterior to the tongue tip in 12 young (20-29 years of age) and 12 elderly (70-79 years of age) subjects. Stimulus duration was 2 s; the sizes of the tongue areas stimulated were 12.5, 25 and 50 mm2. On average, the young subjects were more sensitive to NaCl on the tongue tip than on the more posterior stimulation site and exhibited, at both tongue loci, an increase in detection performance as stimulus concentration increased. The elderly subjects, on the other hand, performed at chance level at both tongue loci for all three stimulus sizes and concentrations tested. No sex differences were observed. In the young subjects, the mean R-index increased monotonically as a function of stimulus size for the two highest NaCl concentrations at both tongue loci. A hyperbolic function provided the best fit to these data at the tongue tip, and an exponential function at the more posterior tongue region, implying a different pattern of spatial summation at these two sites. Overall, this study demonstrates that marked age-related changes in regional taste sensitivity to NaCl are present in elderly persons.