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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY I 



if the insular and temporal cortex of the cat ha\e a 

 significance to the cat's auditory function similar to 

 that of areas i8 and ig and the temporal cortex to 

 the monkey's visual function. Also, though prophecy 

 is a questionable if not dangerous indulgence for 

 ordinary people, one also wonders, given an animal 

 whose sophistication is augmented by the learning of 

 many rather than a single type of auditory discrimina- 

 tion, whether the particular habit (tonal pattern in 

 this case) would remain as firmly corticalizcd. 



Rose & Woolsey (85) introduce in their study an 

 anatomical concept which goes a long way toward 

 clearing up at least one aspect of the interrelationship 

 between the subdivisions of the cat's auditory cortex 

 and also toward providing anatomical support for the 

 work of the Neff group. This is based on the shifting 

 pattern of degeneration observed in the medial genic- 

 ulate body as the cortical lesions are varied in pattern 

 to include one or more of the subdivisions (fig. 6 

 indicates the areas and the terminology applied to 

 them). It is considered that a cortical area receives an 

 essential projection from a given thalamic nucleus if 

 destruction of that area and only that area results in 

 marked degeneration in the thalamic nucleus. If, how- 

 ever, two cortical areas are considered and if destruc- 

 tion of neither of these alone causes degeneration in a 

 given thalamic nucleus, but simultaneous destruction 

 of both does lead to severe degeneration in that 

 nucleus, both cortical areas are said to receive sustain- 

 ing projections from the nucleus. On this basis, Rose 

 & Woolsey found that the only component of the 

 cortical auditory complex which receives an essential 

 projection from the medial geniculate (pars princi- 

 palis) is A I. Since, however, simultaneous destruction 

 of A I, A II, and EP result in much more profound 

 medial geniculate degeneration than does A I alone, 

 it is considered that both All and EP receive sustain- 

 ing projections from the geniculate pars principalis. 

 Even the combination leaves the posterior third of the 

 nucleus relatively unscathed. It is only when the 

 cortical destruction is extended ventrally to include 

 all of the cortex between A II and EP and the rhinal 

 fissure (temporal and insular cortex as shown in fig. 6) 

 that severe degeneration extends posteriorly to include 

 the entire pars principalis. There is, therefore, projec- 

 tion from the posterior sector of the pars principalis 

 to the temporal and insular cortex. That this is 

 probably a sustaining projection is attested by the 

 fact that the still limited evidence indicates insular 

 and temporal lesions alone fail to produce severe 

 posterior sector degeneration. Similarly, the pars 

 magnocellularis degenerates markedly only when A I, 



A II, EP, insular and temporal area'* are all destroyed. 

 Both posterior pars principalis and magnocellularis 

 are largely preserved by the preservation of A I alone; 

 consequently, it would appear that both emit rather 

 widespread sustaining projections, but there is no 

 evidence as yet of emission of essential projections. 

 Finally, from the limited available evidence, the 

 anterior part of the posterior nuclear group of the 

 thalamus, in addition to the medial geniculate, must 

 be suspected of having auditory connections. The 

 critical evidence is lacking but this thalamic area, 

 lying between auditory and tactile nuclei, probably 

 sends a sustaining projection to S II, which itself has 

 ijeen shown to be excitable by auditory stimulation 

 (15, 16, 19, 65, 70). Moreover, this auditory excita- 

 bility, according to Rose & Woolsey (85), .seems to be 

 independent of medial geniculate-auditory cortex 

 activity since it appears even when the medial genic- 

 ulate body is profoundly degenerated. In contrast to 

 this conclusion, Priljram ft al. (73), noting an ap- 

 parently similar system in the monkey, maintain that 

 the responses in S II do drop out upon degeneration 

 of the medial geniculate, and so come to the conclu- 

 sion that the interconnection is by way of collaterals 

 from the medial geniculate. Until this conflict is re- 

 solved, therefore, the question of the essential connec- 

 tion of this thalamic nucleus and cortical area with 

 the cochlear projection pathway must be left open. 



Returning briefly to efforts toward finding some 

 auditory integrative function which is corticalizcd in 

 the sense that the task cannot be accomplished with- 

 out cortical participation, the work of Neff f < al. (67) 

 deserves special attention. They trained cats to make a 

 response requiring localization of sound in space, cor- 

 rect performance being rewarded with food. Lesions 

 were then made in A I in .some cases and A I, A II and 

 EP in others. Bilateral destruction even of A I, if 

 complete, caused severe deterioration of performance 

 in the test situation. That this behavioral deficit was 

 specific to hearing was demonstrated by a normal 

 capacity to learn a problem in the same situation if it 

 were based on visual cues. As the authors point out, 

 while the auditory cortex must play an important role 

 in the function of localization of sound in space, it is 

 less clear what the nature of this role may be. The 

 evidence would allow several hypotheses but select 

 none of them. The authors list the following. /) Intact 

 auditory cortex is essential to learning the relationship 

 between auditory signal and food reward. 2) Intact 

 auditory cortex is essential for maintaining attention 

 to auditory signal, attention being defined as the 

 abilitv of the animal to orient toward the signal and 



