392 W. MAKOUS AND OTHERS 



the wire electrode advances from a primarily gustatory area, the density of 

 neural response to temperature and tactile stimulation will increase due 

 both to an increase in the number of units stimulated by touch and their 

 greater frequency of firing so that the electrophysiological evidences 

 would become more apparent. As the electrode advances still further, 

 zones of overlapping tactile and taste sensitivity gradually give way to 

 areas primarily tactual in nature until taste can no longer be recorded. In 

 the center of the trigeminal nucleus, the response to tactual stimulation 

 of appropriate face parts is much stronger and obvious. 



For those electrode sites that could be histologically verified, the results 

 invariably indicated that taste units lay within the solitary nucleus or just 

 ventral to it. Figure 8 is a tracing of a transverse section through the 

 medulla showing the position of two electrode tracks. Nearly the full 

 extent of the medial electrode track, in which three taste units were isolated 

 (within the black rectangular area), was visible in this one section. For 

 one unit, the receptive area was determined, which proved to be a small 

 point on the anterior tip of the tongue. This agrees with the histological 

 results of Fig. 8, which show the track was in the very anterior portion of 

 the solitary nucleus, to which the anterior tongue projects (Torvik, 1956). 

 One of these three taste units had the lowest quinine threshold that was 

 obtained during the course of this investigation (0-00006 m). The open 

 rectangle of the lateral track shows the location of single units responding 

 solely to tactile stimulation of the tongue. 



SUMMARY 



1. Multiunit recording in the medullas of rats and cats in the anterior 

 solitary tract and its nucleus yielded responses to the application of taste 

 stimuli to the anterior tongue. Histological analysis verified the location 

 of the taste reactive areas in the anterior solitary tract or associated nucleus. 



2. The taste areas of the medulla were contiguous to, and often over- 

 lapped, areas sensitive to tactile and temperature sensitivity of the tongue 

 and general mouth areas which bore a systematic relation to the somato- 

 topic layout of the head and body tactile sensitivity. 



3. Single unit recording in the rat medulla showed that many units 

 displayed a generality of response to a number, if not all, taste stimuli 

 used. In addition, many taste units could also be activated by cooHng 

 and by mechanical stimulation. However, differences in relative frequency 

 of discharge were found among diff'erent chemical stimuli, but no simple 

 grouping or classification of cell types was apparent. 



