TOUCH AND KINESTHESIS 399 



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FIG. 3. Figurine map depicting the representation of the body surface in the ventrobasal thalamic 

 complex of the monkey, Macacus rhesus, constructed from data obtained in an evoked potential experi- 

 ment under deep barbiturate anesthesia. Inset drawing shows diagrammatically the thalamic struc- 

 tures in a Horsely-Clarke plane ^frontal plane 6). Dots indicate points at which electrical activity 

 was evoked by tactile stimulation of the body surface. For each dot in the inset an appropriately 

 located figurine is shown. No responses were obtained elsewhere along the explored electrode tracks. 

 Body areas, stimulation of which evoked large, smaller or small responses are shown in the figurines 

 by solid black, cross-hatching or diagonal lines, respectively. The body is represented contralaterally 

 except for the face and intraoral structures which are bilaterally represented. Numerals indicate the 

 mediolateral and vertical Horsley-Clarke coordinates. MD: raediodorsal nucleus; CM: centrum 

 medianum; GLD: dorsal lateral geniculate body; VBarc: arcuate component of the ventrobasal 

 complex; VBex: external component of the ventrobasal complex; VM: ventromedial nucleus; /.- the 

 inferior portion of the ventral nuclear group. [From Mountcastle & Henneman (185).] 



facial regions. Whether this projection depends upon 

 ipsilaterai axons from the main sensory nucleus 

 traveling in the dorsal trigeminal tract is conjectural 

 (see p. 398). 



Patterns in Thalamic Relay Nucleus 



DEFINITION OF TH.^L.^Mic RELAY NUCLEUS. Evidence 

 from several experimental approaches indicates that 



the ventrobasal complex, consisting of an external 

 and an arcuate portion, is the thalamic relay for the 

 medial lemniscal system. Tactile and kinesthetic ac- , 

 tivity is relayed through it to the first somatic area of 

 the cortex. In carnivores and priinates this region of 

 the thalamus is distinguished from its neighbors in 

 the ventral thalamic group by a special cytoarchi- 

 tecture. It contains neurons which vary widely in size. 

 These sizes are grouped around two means, though in 



