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ROBERT M. BENJAMIN 



1962). The projections of the tongue nerves (Fig. 3) are more complex 

 in this animal, but only a few points need be mentioned for this discussion. 

 On the ipsilateral side the relationships are much like those in the rat. 

 Anteriorly, there is a place for taste medial to the lingual nerve projection. 

 On the contralateral side, however, there seems to be no place for an inde- 

 pendent taste area. Not only is there complete overlap of all the responses, 

 but the taste nerve projections do not even reach the medial tip of the 

 nucleus. These data would seem to preclude spatial independence for taste 

 in the squirrel monkey unless the taste input turned out to be purely 

 ipsilateral in this animal. This eventuality seemed unhkely in view of the 

 bilaterality of effects from human cortical lesions (Bornstein, 1940). 

 Nevertheless, a subsequent single unit analysis (Fig. 4) estabhshed that 

 taste was, indeed, ipsilateral. Notice that all the taste units (solid circles) 

 have been plotted in the ipsilateral ventromedial nuclear complex. This 

 laterality was conclusively established for all except five of the units which 

 had receptive fields on the extreme back of the tongue. Independence is 

 maintained, but unhke in the rat, the separation shifts from a medio- 

 lateral plane anteriorly, to a dorso-ventral plane posteriorly. 



It is clear, then, that in both the rat and squirrel monkey thalamus the 

 taste system is spatially separated from other tongue modalities. 



Thus far taste units have been discussed as if they responded exclusively 

 to taste stimuli. Actually, this was not the case, especially in the rat (Table 

 1). All of the units tested (13 of the total 18) also fired when extremely cold 

 water was flowed on the tongue. The response of one unit is shown on a 

 frequency vs. time plot in Fig. 5. The stripped bar shows the resting 



Table 1. Summary of units localized in 

 the thalamus of the rat and squirrel 

 MONKEY. Only 13 of the 18 taste-tempera- 



TURE UNITS IN THE RAT WERE ADEQUATELY 

 TESTED FOR A TEMPERATURE RESPONSE. 



activity of the unit at 2 to 3 impulses/sec. The unit responded to a " white " 

 taste solution (an atrocious mixture of quinine, sodium chloride, hydro- 

 chloric acid, and sucrose) in a slowly adapting, tonic fashion. The unit 



