CHEMICAL CODING IN T ASTE — TE MPOR A L PATTERNS 277 



0.01 M NaCl was 15 per cent of peak magnitude. In contrast, the response 

 to 0.1 M NaCl, shown here on the right, was 78 per cent of peak magnitude 

 10 sec post-peak. Four minutes post peak, this response to 0.1 m NaCl 

 was 58 per cent of peak magnitude. 



Fig. 2. Summated neural responses recorded from the entire chorda tympani 

 nerve of one rat following chemical stimulation of the anterior portion of the 

 tongue. The record is continuous, and reads from right to left. Downward 

 deflection of the signal line, at the top of the record, indicates duration of 

 chemical flow through the flow system and closed tongue chamber. The signal 

 line has been retouched. 



For the rats studied to date, the median response to 0.1 M NaCl at 20 

 sec post peak was 86 per cent of peak magnitude. After the same period of 

 time, the median response to 0.01 m NaCl was 34 per cent of peak magni- 

 tude. About 4 min post peak, 0.1 m NaCl was down to 67 per cent, while 

 0.01 M had a median adapted level of 27 per cent of peak magnitude. 

 Responses to 0.05 NaCl appeared to decrease faster than those to 0.1 m 

 NaCl but slower than the responses to 0.01 m NaCl. Thus, under these re- 

 cording conditions, rate and degree of adaptation of NaCl responses appear 

 to decrease as stimulus concentration increases. 



Recently, it has been observed that tongue stimulation with amino acids 

 can produce responses in the rat chorda tympani with time courses dif- 

 ferent from the responses to NaCl (Halpern et al., 1961). The response 

 magnitude produced by amino acids such as glycine and the stereoisomers 

 of alanine are generally smaller than the rat chorda tympani response to 

 0.05 M NaCl (the response to 3.0 m glycine is between 0.05 m NaCl and 0. 1 m 

 NaCl) (Fig. 3a, b). 



Oscillograph records indicate that responses to 1.5 m glycine and 1.2 m 

 DL-alanine build up to peak magnitude slowly and do not have the initial 

 large spike, high frequency burst found with responses to 0.1 m NaCl 

 (Figs. 4, 5). In addition, responses to 1.5 M glycine and 1.2 M DL-alanine 

 have post peak magnitudes much closer to peak magnitude itself than do 

 responses to 0.1 m NaCl. Summator records (Figs. 6, 7, 8) likewise demon- 

 strate slow rise times and well maintained responses for these amino acids. 

 Time to peak magnitude appears to be a function of concentration, type 

 of amino acid, and configuration (Fig. 9). 



20 



