386 



W. MAKOUS AND OTHERS 



of the solitary tract (Allen, 1923 ; Brodal et al. 1956 ; Torvik, 1956 ; 

 Winkler and Potter, 1914) throughout most of the area studied. In Fig. 5, 

 a section containing two 130// electrode paths is shown. Gustatory 

 activity was observed in the left electrode path, shown here ending at the 

 bottom of the solitary tract. In adjacent sections, this path was seen to 



30 



25 



LiJ 



Q 20 



^ 15 



UJ 



if) 10 



-z. 

 o 



CL 







2.0 2.2 2.4 2.6 2.8 3.0 



DEPTH (mm.) 



Fig. 4. Maximum relative summated neural response to chemical, thermal, 

 and tactile stimuli as a function of electrode depth in a single electrode track. 

 The response magnitude is measured from the prestimulus level to the highest 

 point reached by the response ; depth of electrode tip below surface of the 

 medulla was taken from the micromanipulator co-ordinates. The stimuli 

 were: taste, 0-03 m HCl at approximately 28 C ; warm, distilled water at 

 approximately 38 'C ; cold, distilled water at approximately 18'C; and tactile, 

 stroking the tongue with a camel's hair brush soaked in distilled water at 28°C. 



pass through the lateral edge of the lateral solitary subnucleus. The other 

 path, cutting through the medial edge of the medial solitary subnucleus, 

 showed no gustatory activity. In a total of some 50 electrode penetrations 

 studied histologically, 20 positive responses (11 definite, 9 questionable) 

 were seen to pass through the solitary tract or its lateral subnucleus or to 

 interrupt fascicles entering the solitary tract. Of 30 unresponsive place- 

 ments, 8 were observed to penetrate the solitary tract or lateral subnucleus, 

 8 were located in the medial subnucleus, and 14 were located in other 



