CENTRAL AUDITORY MECHANISMS 



599 



carry through its appropriately directed activity until 

 the full response of opening a door and obtaining; food 

 is accomplished, jj) Intact auditory cortex is necessary 

 for accurate localization of sound in space. As indi- 

 cated above, the data fail clearly to single out any of 

 these. This, incidentally, is a common finding in 

 behavioral experiments involving extirpation ot brain 

 tissue. It may be an inherent failing in all such ex- 

 periments. However, this is of more concern from the 

 standpoint of the neurology of learning than from that 

 of specifically auditory integration. 



We cannot leave the subject of definition of the 

 auditory area without referring to the work of 

 Lilly (55, 56) who has introduced a new method 

 and a new dimension to this field of study. Using a 

 square array of 25 electrodes covering an area of 

 cortex of i cm'-, 25 amplifiers and glow tubes, each 

 channel serving one electrode, and photographing 

 at 128 frames per sec. the bank of glow tubes, Lilly 

 has been able to demonstrate the patterns of spon- 

 tanous electrical activity and those evoked by acous- 

 tic stimulation in the cat's auditory cortex. In this 

 fashion, the simultaneous cortical surface activity 

 can be recorded at 25 different zones and the changes 

 at each noted in time sequence. Thus Lilly has 

 demonstrated what he calls 'forms and figures' of 

 cortical activity which combine the dimensions of 

 time and space in a way not previously possible. 

 The array was placed across the upper end of the 

 posterior ectosylvian sulcus so that it covered part 

 of the junctional area of A I and A II with EP. 

 Lilly found that both spontaneous activity and the 

 response to clicks followed a definite, repeatable 

 pattern. Under deep anesthesia the response to clicks 

 would appear first in one corner of the array, spread 

 posteriorly to a boundary and there die out. Pos- 

 terior to the boundary (i.e. in EP) spontaneous 

 waves tended to originate and travel downwards 

 along the posterior ectosylvian gyrus; however, 

 under lighter anesthesia the response wave could 

 trigger the 'spontaneous' EP waves, and at still 

 lighter levels spontaneous waves were seen to origi- 

 nate in A I and travel across the border. In another 

 series of experiments on unanesthetized monkeys, 

 clicks set ofT waves of activity which were observed 

 to travel systematically over the sensorimotor cortex. 

 Thus, Lilly has at once made several interesting 

 points, some of which are of specific interest in the 

 development of knowledge of the cortical auditory 

 equipment and others are of even greater significance 

 to neurophysiological thinking in general. With 

 respect to auditory function, he has shown that there 



is a certain validity to the accepted subdivision of 

 auditory cortex, albeit this may have been to some 

 degree overplayed in the past because most previous 

 workers (with one qualified exception in Bremer') 

 have used deeply anesthetized animals as the stand- 

 ard preparation. At the least, these studies present 

 the interrelationship of auditory subdivisions from a 

 new \iewpoint. He has further demonstrated that 

 the excitation of cerebral cortex which results from 

 acoustic stimulation may be (or perhaps always is) 

 considerably more widespread than is usually as- 

 sumed, tacitly at least, in the plan of auditory ex- 

 periments. This is somewhat disquieting from the 

 standpoint of planning an experiment to demon- 

 strate by electrophysiological method some facet of 

 cortical auditory function; howe\er, it is perhaps 

 potentially comforting in even greater degree to 

 those who work with behavioral methods and are 

 constantly confronted with the necessity of explain- 

 ing why an animal in which access to cortical in- 

 tegrative processes has presumably been denied to 

 the acoustic system (by remoxal of receptive areas) 

 can yet behave as though auditory stimulation still 

 held meaning for him. 



From a more general \iewpoint, Lilly has neatly 

 demonstrated the restrictive elTect of anesthetization 

 on cortical activity with respect to both time and 

 space such that the functional separation of con- 

 tiguous areas tends to be exaggerated. It should be 

 an ample indication that while unguarded use of 

 anesthesia in electrophysiological studies of the 

 cortex may relieve some technical problems for the 

 experimenter, it may simultaneously furnish the 

 basis for an abundance of conceptual 'red herrings.' 

 Lilly's work suggests further, however, that the en- 

 lightened, controlled use of anesthesia may be of 

 most positive value in cortical studies by virtue of 

 its capacity to separate functional areas whose 

 boundaries tend to be inconspicuous in the waking 

 animal. 



The reader will note that, having begun with a 

 hazy idea of the location and limits of the auditory 

 cortex of the cat, these gradually became sharply 

 defined through the years with improvement in 

 instrumentation, method and thinking. At several 

 points in this history, the matter seemed to have 

 been settled. Each time this has occurred, someone 



' Bremer's encephale isole preparation falls short of qualifying 

 as equivalent to the intact preparation to the extent that it 

 interrupts part of the reticular input; however, it is different 

 from the deeply anesthetized animal to the extent that part of 

 the reticular system is intact. 



