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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY I 



were suggestive that this might be so in primates. 

 Recent findings in rat (283, 285, 286), cat (284) and 

 dog (10, 11) provide acceptable evidence for this 

 statement. Ablations of somatic areas I and II to- 

 gether led to findings which may but need not be 

 discordant. In the rat (283, 286) discrimination of 

 roughness can apparently be relearned and form 

 discrimination need not be lost after such ablations. 

 Likewise form can be discriminated satisfactorily by 

 the monkey with some retraining (143), even though 

 a severe loss of tactile acuity is evident when placing 

 reactions or grasp reflexes are tested. On the other 

 hand, in the cat (284) and dog (i i) a persistent in- 

 ability of the animal to discriminate somesthetic 

 stimuli has been reported after such combined re- 

 movals. The findings in the cat can be dismissed since 

 they are based on studies on one animal only. The 

 findings of Allen on the dog require some comment. 

 It appears from his description that the actual cortical 

 removals exceeded considerably the anatomical limits 

 of SI and SII. This might but probably does not 

 account for Allen's divergent findings. What seems to 

 be a more probable explanation of his results is that — 

 in contrast to all other obsersers here considered who 

 used a pair of discriminanda differing only in weight, 

 roughness or form — Allen alone employed a differ- 

 ential conditioning technique to test the somesthetic 

 defects of his animals. The response of the animal 

 consisted of lifting his foreleg to a positive stiinulus 

 and not lifting it to a negative one. The positive and 

 negative stimuli were respectively a light stroking of 

 the iwck with the grain and against the grain or a 

 light stroking with the grain once a second (positive) 

 and three times a second (negatixe). The chief defect 

 observed was the inability of the operated animals to 

 withold the foreleg response when negative stimuli 

 were applied. The response to positive stimuli was 

 retained without impairment. In short, after the oper- 

 ations the animals tended to lift the leg to both the 

 negative and po.sitive stimuli and could not be re- 

 trained to make the differentiation. Since the task .set 

 by Allen for his animals was quite difi"erent and prob- 

 ably more subtle than those set by the other observers, 

 the different results need not imply contradictory 

 findings. 



Even though older anatomical and physiological 

 views have often held that the precentral and post- 

 central regions somehow form a functional unit of a 

 higher order, it is only recently that the effects of 

 postcentral and precentral ablation upon the somes- 

 thetic capacity of the monkey have been tested with 

 modern techniques. As already mentioned, Kruger & 



Porter C'43) found no permanent deficits in somes- 

 thetic form discrimination after remo\al of the somatic 

 areas I and II in their monkeys even though a severe 

 tactile impairment of the limbs could be reasonably 

 inferred to be present. Likewise, there was a perfect 

 retention of the learned habit if the precentral gyrus 

 alone was removed despite the .severe motor deficits 

 in the limbs. However, if both these regions were re- 

 moved jointK on one side the two animals tested 

 could not be trained to discriminate with the contra- 

 lateral hand a three dimensional figure ' L' from its 

 in\ersion. However, a \isual discrimination task could 

 be carried out utilizing that limb. Since this work re- 

 ports permanent deficits, further studies along these 

 lines are urgently needed. The reported lesions ex- 

 tended farther caudally than the anatomical limits of 

 areas i to 3. It remains to be determined whether an 

 inclusion of at least a part of the parietal region is 

 necessary to produce permanent discrimination def- 

 icits. 



The knowledge that some tactile responses from the 

 ipsilateral side of the body reach the ipsilateral cortex 

 (although we believe this is not true for the first 

 somatic field) could suggest that learning; of at least 

 simple somesthetic discriminations takes place simul- 

 taneously in both hemispheres. Stamm & Sperry's 

 (22B) results are, therefore, somewhat surprising. In 

 their cats the discrimination of form, softness and 

 roughness performed with one paw had to be com- 

 pletely relearned only if the corpus callosum was 

 sectioned. Clearly more data are needed to substanti- 

 ate and further elucidate this problem. 



The last set of available data we wish to consider 

 pertains to findings after lesions of the parietal cortex. 

 It was already suggested b\ the older work (21 1-2 13) 

 that parietal lesions may produce some deficits in the 

 capacity to discriminate somesthetic cues even though 

 the animals could usually relearn the tasks. Such 

 deficits after ablations of the parietal cortex which 

 spared the postcentral region itself were definitely 

 established by Blum (23), Blum et al. (24) and Pribram 

 & Barry (199). Blum et al. (24) made the tentative 

 suggestion that processes which determine the somes- 

 thetic discrimination capacity of the animal take place 

 outside the postcentral region itself and specifically in 

 the parietal region. The available findings hardly per- 

 mit an evaluation of this suggestion. The data at hand 

 are as yet too few in number, too limited in scope and 

 not sufficicntU systematic with respect to .some corti- 

 cal fields which are probably or possibly relevant. 

 Some important observations, therefore, are subject 

 to different interpretations. For example, the im- 



