SOME THALAMIC AND CORTICAL MECHANISMS OF TASTE 323 



and, of course, a taste deficit. The dots emphasize that the degeneration 

 was not complete ; many normal cells remained throughout the degenerated 

 area. If the lesion spared the ventral part of the composite area (cases 2 

 and 4) discrimination remained normal and so did the medial part of the 

 subnucleus. Conversely, a ventral lesion (case 3) was associated with a 

 taste deficit and medial degeneration. 





Deficit 



Normal 

 Deficit 



'"^ 'iiL ^:3 Normal 



Fig. 13. Diagrams of some sample cortical lesions in the rat, the associated 

 retrograde thalamic degeneration, and postoperative status of taste discrimina- 

 tion. The composite taste nerve area is outlined. All lesions were bilaterally 



symmetrical. 



All of the data from the rat fit together rather well. The ventral part of 

 the taste nerve area, which is most crucial for taste behavior, receives pro- 

 jections from the medial part of the thalamus where, as we have seen, 

 microelectrode studies have localized the taste cells. I should add that 

 severe taste impairment results from thalamic lesions placed directly in this 

 medial part (Abies and Benjamin, 1960 ; Benjamin, 1960 ; Oakley and 

 Pfaff'mann, 1962). 



Finally, to complete the picture, this localization of cortical taste function 

 in the American rat is quite compatible with the localization of the taste 

 units in the cortex of Swedish cats (Cohen et al., 1957 ; Landgren, 1958). 



We would still be complacently happy had we not tried the same type of 

 experiments on the squirrel monkey. Lesions of the taste nerve areas in 

 this animal do not produce consistent taste impairment nor do they produce 

 degeneration of the proper part of the thalamus. 



Figure 14 shows the evoked potential areas of the various taste nerves 

 in the squirrel monkey. Electrical stimulation of the chorda tympani nerve 

 (Benjamin and Emmers, 1960) produced not one area, as in the rat, but 

 two areas. The posterior one was situated right in the middle of the lingual 

 nerve area though this is not illustrated on the figure. The other chorda 

 area, drawn in black, was situated anterior to the Hngual nerve projection 



