NaCl thresholds: relationship to anterior tongue locus, area of stimulation, and number of fungiform papillae

NaCl detection thresholds were determined for 12.5- and 50-mm(2) lingual areas at four anterior tongue locations in eight subjects using a device that allowed for accurate temporal and spatial presentation of tastants to small regions of the anterior tongue. The locations, all on the right side of the tongue, were the tongue tip, an area 1.7 cm posterior to the tongue tip, and regions 1.7 and 3.4 cm posterior to the tip along the tongue's lateral margin. Stimulus duration was 0.75 s. Thresholds were established using a two-alternative forced-choice single-staircase procedure, and the number of fungiform papillae at each stimulation site was counted with the aid of videomicroscopy. NaCl thresholds were lower for the 50-mm(2) than the 12.5-mm(2) stimulation area at all target sites, and were directly related to papillary number among and within the stimulated regions. For a given number of papillae, thresholds were lower within the 12.5-mm(2) than within the 50-mm(2) stimulation region, likely reflecting taste bud density and activation of common afferent pathways. The tongue tip was more sensitive than any other tongue region, and the lateral margins were seemingly more sensitive than the lingual centrum. Large individual differences in taste sensitivity and tongue papilla numbers were noted, and some subjects were insensitive to the highest tastant concentrations at the nontip loci. This study empirically demonstrates that NaCl detection sensitivity varies across discrete regions of the anterior tongue and is related to the relative number and density of fungiform papillae.