CENTRAL AUDIT(JRV MECHANISMS 



597 



FIG. 6. Composite view of all areas of cat brain showing 

 auditory function. A I, first auditory area; A II, second auditory 

 area; EP, posterior ectosylvian area; S II, second somatic area; 

 IN, insular region; TE, temporal area. 



thalamic degeneration in their cat.s. The rcsuhs in 

 this series of experiments differ from those of Meyer 

 & Woolsey in that ability to discriminate frequency 

 was not permanently impaired even after complete 

 lesions of A I, A II, EP and S II. Three significant 

 points in explanation of the apparent discrepancy 

 were offered by Butler et al. /) The testing methods, 

 as have already been mentioned above were different, 

 r) In the Meyer-Woolsey animals with loss of dis- 

 crimination, the lesions, though listed as including 

 A I, A II, EP and S II, actually extended ventrally 

 nearly to the rhinal fissure (unlike those of Butler et 

 al.^. j) In the latter group, the posterior part of the 

 medial geniculate, pars principalis, consistently es- 

 caped degeneration, although it was also noted that 

 the nearer to the rhinal fissure the lesion approached, 

 the farther posterior crept the degeneration in the 

 medial geniculate. Thus, the tissue lying before and 

 behind the p.seudosylvian sulcus, hitherto largely im- 

 mune to implication in the auditory cortical sphere, 

 began to take on a most suspiciously acoustic flavor. 

 That this trend is essentially correct has been demon- 

 strated in recent experiments by Neff and his group 

 and in the recent critical analysis by Rose & Woolsey 

 (86) of thalamic degeneration resulting from lesions 

 of the several subdivisions of auditory and apparently 

 related cortex singly and in combinations. 



Diamond & Neff (24) trained cats to respond to 

 change in a simple tonal pattern. A three-tone se- 

 quence, for example, of low-high-low was presented 

 repetitively for a variable number of tiines and then 

 changed abruptly to high-low-high, at which point 



the animal, in the course of trairiin^, learned to 

 respond (by moving across the middje of a shuttle 

 bo.x) to avoid shock. Extirpation qf A I failed to 

 disturb the habit of discriminating tht; two patterns. 

 With extensive damage to A II and EF in addition to 

 -A I, the habit wa"; temporarily lost but could be re- 

 established by further training. If the destruction of 

 all three areas was complete, the tonal pattern dis- 

 crimination could not be re-established even with a 

 prolonged period of retraining. It is interesting to 

 note that even small remnants of tissue which could 

 be excited by sound, and which closely adjoined 

 ablated areas, were sufiicient to make possible retrain- 

 ing of the tonal pattern discrimination. In a second 

 series of experiments, Goldberg et al. (39), having 

 trained cats to both a simple frequency discrimination 

 habit and to the tonal pattern discrimination, now 

 extirpated bilaterally the region ventral to A II and 

 EP (insular and temporal cortex shown in fig. 6), 

 sparing A I, A II and EP as demonstrated by subse- 

 quent responsiveness to click stimulation and absence 

 of severe degeneration in the medial geniculate. The 

 results were quite surprising, both simple tone dis- 

 crimination and tonal pattern discrimination being 

 lost after operation. It proved possible to re-establish 

 simple discrimination in about the same time as that 

 required for original training. On the contrary, pat- 

 tern discrimination could not be relearned even with 

 prolonged retraining. The behavior of the animals in 

 the test situation was not visibly different from pre- 

 operative behavior and, since the frequency discrimi- 

 nation habit was relearned, one cannot attribute the 

 results to loss of learning capacity; rather the loss of 

 pattern discrimination seems to be a specific auditory 

 deficit. 



Two salient features, then, emerge from the recent 

 work of Neff and his group. /) The insular and tem- 

 poral cortex of the cat are demonstrated to be of 

 crucial importance to at least some aspects of auditory 

 integrative function. 2) Discrimination of tonal pat- 

 terns (as distinguished from simple change in fre- 

 quency) appears to be cortically bound. 



One cannot help recalling (at least this author 

 cannot) experiments in x'isual discrimination (4, 7) in 

 which somewhat similar results were obtained after 

 lesions of areas 18 and 19 and the temporal lobe in 

 the monkey. It suijsequently proved, however, that 

 losses of discriminative ability in the monkey were less 

 permanent if the monkey had been trained to learn 

 quickly many different visually-guided discrimina- 

 tions rather than just one (81, 82). Although the 

 evidence is insufficient, one cannot help but wonder 



