THE GUSTATORY RELAY IN THE MEDULLA 



391 



Stimulation of the tongue, while 21 out of 24 units responded to cool tap 

 water (9°-12°C). In fact, from the present data, the generalization could 

 be made that any given second order taste unit in the rat will respond to 

 cooling of the tongue with water, provided the unit has a certain minimal 

 level of reactivity to chemical stimulation. These observations seem at 

 variance with the results with wire electrodes (see Fig. 1) showing that 

 certain loci are primarily responsive to gustatory stimuli. Such areas give 

 relatively little response to cooHng or brushing the tongue, whereas other 



Fig. 8. Histological loci of microelectrode tracks in animal 10,361. Magnifica- 

 tion 22-8 X. Thirty micron frozen section, cresyl violet stain. C.r., restiform 

 body ; C.t., trapezoid body ; M.v.n., medial vestibular nucleus ; N. VII, 

 motor nucleus of seventh cranial nerve ; N. VIII, dorsal cochlear nucleus ; 

 N.f.s., nucleus of the solitary tract ; N.o.V., nucleus oralis of spinal trigeminal 

 complex ; N.pr.V., main sensory nucleus (nucleus principalis) ; P., pyramids ; 

 TR.sp.V., spinal tract of the trigeminal nerve. 



contiguous points inay give definite responses to both tongue tactile and 

 temperature stimulation as well as taste. Two factors might account for 

 this apparent discrepancy. In the first place, not all gustatory units respond 

 to temperature or touch. Thus, the density of units so activated is relatively 

 less than that activated by taste solutions. Secondly, the relative frequency 

 of response to the so-called " inadequate " touch and temperature stimuli 

 is often lower than that produced by taste solutions in the same elements. 

 In a sense, the tactile and temperature responses may well be lost in 

 physiological background with gross electrodes, whereas single unit 

 recording may be more effective in picking up moderate responses. As 



