CHEMICAL CODING IN TASTE— TEMPORAL 

 PATTERNS 



Bruce P. Halpern 



Department of Physiology, State University of New York, 

 Upstate Medical Center, Syracuse 10, New York 



Much careful consideration has been given to the relationships between 

 the chemical characteristics of gustatory stimuli and the magnitude of the 

 neural response, i.e. the maximum or peak magnitude of the response to 

 stimuli. There has been considerably less interest in the relationships 

 between stimulus characteristics and changes in response magnitude over 

 time. 



The temporal characteristics of gustatory neural responses have been 

 studied for only a few chemicals. Sodium chloride has received the most 

 attention. A number of workers (Beidler, 1953, 1955, and 1961 ; Pfaff- 

 mann, 1955 ; Zotterman, 1956 ; Fishman, 1957 ; Halpern et a/., 1961) 

 have reported that the response to NaCl recorded from the rat chorda 

 tympani shows a rapid rise to peak magnitude, a brief initial transient, 

 and then a rapid fall to a relatively maintained response level. The latter 

 is generally considered the adapted response level. In contrast, human 

 psychophysical responses to NaCl have been reported to fall to or near 

 zero quickly, sometimes within 10 sec (see : Pfaflfmann, 1959, p. 37 ; 

 Beidler, 1961, p. 124). Therefore, it has been proposed that gustatory 

 responses in the CNS may be less well sustained than in peripheral nerves 

 (Beidler, 1953, 1961). Before considering peripheral nerve responses in 

 detail, let us briefly compare chorda tympani vs. CNS gustatory responses. 

 Figure 1 is summated neural responses to stimulation of the anterior 

 portion of the rat's tongue with 0.1 m NaCl. The records read from right 

 to left. The lower record was made from the whole chorda tympani nerve. 

 The multiunit neural activity was led off the nerve through silver-silver 

 chloride wick electrodes. Here, and in subsequent figures, 25 ml of stimu- 

 lating solution flowed through the tongue chamber and over the tongue in 

 approximately 8 sec. The neural activity was passed through a Grass P-5 

 a.c. preamplifier, then led through a separator, which was set to remove 

 much of the background noise, and then into a summator. The summator 

 rise time was usually 0.75 sec. The fall time was always 7.5 sec. The 

 summator output drove a critically damped Texas recti-riter. The upper 



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