DYNAMICS OF TASTE CELLS 147 



Under these assumptions the response pattern of a particular neuron 

 does not necessarily correspond to the pattern of chemical sensitivity that 

 it transmits to the receptor cell. The receptor cell may receive sensitizers 

 from more than one neuron and we cannot assume that they will be the 

 same. The pattern of centrifugal information is determined by the central 

 connections of each neuron while its response pattern is determined by the 

 complete pattern of sensitivity of the receptor cell. 



The differences between the efferent and the afferent patterns brought 

 about by overlapping innervation represent false information or " noise " 

 in the afferent message to the central nervous system. We can assume 

 that this noise is largely eliminated by the familiar principle of mutual 

 inhibition which enhances contrast in the auditory, visual, cutaneous and 

 muscular systems. If only there is some initial bias in the central connec- 

 tions of each sensory neuron, such as might well arise from its spatial 

 relations to the ultimate gustatory centers, and if these biases are different 

 for different neurons, there will be corresponding, although somewhat 

 reduced, biases in the patterns of sensitivity of the receptor cells. 



We have assumed that the intensity of the efferent chemical message is 

 proportional to the richness of innervation, i.e. the number of synaptic 

 contacts, both centrally and peripherally. The probability of excitation of 

 nerve impulses also obviously depends on the richness of innervation, 

 according to the principle of summation of electrotonic effects. The dis- 

 tribution of afferent impulses among the sensory neurons is therefore 

 automatically biased in exactly the right way to excite preferentially th^ 

 center that corresponds to the particular class of chemical compound 

 that happens to be the external stimulus at the moment. The situation is 

 clearest near threshold when only the receptor cells that are richly supplied 

 with the proper chemical sensitizer will develop significant receptor poten- 

 tials and only the neurons that have supplied that sensitizer richly will 

 have enough synaptic contact with those receptor cells to be excited. If 

 the stimulation is stronger, another neuron that may be biased toward 

 another quality will also be excited by the same receptor cell, but it will 

 discharge at a lower rate. But these " unwanted " impulses are made in- 

 effective centrally by the inhibition from the " right " center that is more 

 strongly activated. 



I believe that this niodel of the organization of the gustatory system 

 deserves attention because it makes no assumptions that do not have close 

 counterparts elsewhere in neurobiology and because it explains simul- 

 taneously two puzzling features of gustatory physiology. The first puzzle is 

 the maintenance of neural organization in the presence of rapid turnover 

 of receptor cells in the taste buds. The second is the decoding of the com- 

 plex variety of patterns of response that are found in the single afferent 

 fibers. 



