A peripheral neural correlate of the human fungiform papillae salty, insipid sensations

Neurophysiological research in several different laboratorieshas revealed the existence of a Na-, Li-specific peripheraltaste system in mammalian herbivores and omnivores, but notcarnivores. The presence or absence of this system is readilydetectable in the behavior of the animals towards NaCl solutions.It is proposed that the human has an identical system, and thatactivity within this system is largely, but not entirely, responsiblefor the elicitation of the human sensations of salty and insipid.Under normal conditions, neurons in this system display highlevels of spontaneous activity due largely to salivary Na. Solutionswith Na exceeding the salivary Na level will excite the neuronsand be perceived as salty. Solutions with Na levels less thanthat of the saliva will inhibit the neurons and be perceivedas insipid. The existence of this system in humans is attestedby the fact that human behavior towards NaCl is similar to thatseen in the rat and sheep. The stimuli eliciting the human saltysensations are, in most respects, similar to those active inthe animal experiments with one exception: KCl, the chloridesalt most inactive on animals, elicits a fairly strong saltysensory component. To partially resolve this discordance, itis suggested that the human salty sensation is the result ofhigher order neural activity that involves another peripheraltaste system.