SOME THALAMIC AND CORTICAL MECHANISMS OF TASTE 315 



also responded to 12 C water, but only phasically. This duplicity of res- 

 ponse probably does not represent a convergence of modalities at the 

 thalamus for single peripheral taste fibers in the rat behave in a similar 

 fashion (Fishman, 1957). 



30 



25 



20 



a I5H 



to 



LlI 



"^ lOH 



UNIT 6! -335-5 



"WHITE" TASTE 

 12" C H,0 



I 2 3 4 5 6 7 



SECONDS AFTER STIMULUS ONSET 



Fig. 5, Frequency plot of the responses of a single thalamic neuron in the rat to 

 solutions flowed onto the tongue. 



Most squirrel monkey taste units did not show this duplicity of response 

 (Table 1). Only three of twenty-seven taste neurons responded to tem- 

 perature stimuli. 



Species differences in the response of taste neurons to taste solutions are 

 not uncommon, just difficult to explain. But why should taste neurons 

 respond to temperature in one animal and not in another? One cannot 

 attribute the separation of taste and temperature to a general phylogenetic 

 superiority for the squirrel monkey mixes some modalities as well. This 

 animal had a large proportion of " mechanical " neurons which also res- 

 ponded to temperature whereas the rat tended to keep these separate. 



As in the case of the rat taste units, the bimodality of the mechanical- 

 temperature units in the squirrel monkey probably does not represent 

 convergence at the thalamus. Hensel and Zotterman (Zotterman, 1959) 

 have described similar bimodal single fibers in the lingual nerve of the cat 

 and have shown that their response to temperature stimuli is quite dif- 

 ferent from the response of unimodal temperature fibers. The same 

 difference is characteristic of these squirrel monkey thalamic neurons. I 

 would like to show you a typical sample of each which is truly typical. The 

 responses will be presented in the form of interspike interval dot patterns, 

 a unique and powerful method of data representation described by Wall 

 (1959). First, for purposes of clarification let me interject Fig. 6 which 



