384 W. MAKOUS AND OTHERS 



component, is projected in a topographical manner consistent with that 

 of the somatosensory system. 



MULTIUNIT ACTIVITY IN CAT MEDULLA 



In studying the activity in the cat medullas, nichrome wire electrodes 

 either 30 or 130/^ in diameter, insulated except for the tip, were employed. 

 The oscillograph output was monitored continuously by an audio channel 

 and an integrator-inkwriting recorder. The magnitude of deflection of 

 the latter provided a visual and quantifiable record of the amount of 

 multiunit activity surrounding the tip of the electrode. Stimuli were 

 presented either from polyethylene wash bottles or by a funnel, stopcock, 

 and gravity flow system which flowed over the anterior part of the animal's 

 tongue protruding from the side of the mouth. Thermal stimulation was 

 provided by water at the approximate temperatures : warm, 38°C ; 

 cold, 18"C ; and room temperature, 28°C. Tactile stimulation consisted 

 of stroking the tongue with a brush. Figure 3 shows a record from an 

 active gustatory site in the cat's medulla. 



The form of the responses obtained were similar to those observed in 

 the cat periphery (Liljestrand and Zotterman, 1954 ; Pfaff'mann, 1941 ; 

 Zotterman, 1935). The response to 1 -0 m sucrose solution was no greater 

 than that to distilled water. This response to distilled water, often referred 

 to as " water taste " (Zotterman, 1958), was especially strong following 

 HCl and KCl. 



In the five penetrations in which the relationship among tactile, chemical, 

 and thermal responses was studied quantitatively, responses to taste 

 stimuli usually appeared most dorsally ; tactile responses were never 

 observed dorsal to the most dorsal chemical response. Definite chemical 

 responses occurred in two far medial electrode placements where no tactile 

 responses were observed at any depth, but in other instances both tactile 

 and chemical responses occurred at the same site. The relationships of 

 the responses to chemical, thermal, and tactile stimuli in a single track 

 are shown in Fig. 4. The maximum responses to thermal and chemical 

 stimuli occurred at the same depth in the three preparations tested ; the 

 maximum responses to tactile stimulation occurred at least 0-2 mm more 

 ventrally. 



The maximum extent of the taste area measured • 7 mm rostro- 

 caudally, 0-4 mm medio-laterally, 0-8 mm dorso-ventrally. The center 

 of the chemically responsive area, corrected (Horsley and Clarke, 1908) 

 for a cat skull 880 mm long and 42 mm wide, was located 5-2 mm rostral 

 to the obex, 3-2 mm lateral to the midline, and 2-4 mm ventral to the 

 surface of the medulla. According to Wall and Taub (1962), the cat's 

 nucleus oralis of the trigeminal nucleus is dominated by tactile sensitivity 



