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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY I 



Observations of the responses of cats to electrical 

 stimulation of the brain, such as movements of the 

 ears and turning of head and eyes, led Ferrier to 

 identify as auditory in function the ectosylvian region. 

 This area has remained the ' auditory area' ever since, 

 although the exact limits of the cortex so designated 

 have varied considerably with variations in method, 

 investigator and, presumably, also with variation in 

 the cat itself. For if there is one single incontrovertible 

 fact which has emerged from a long series of investi- 

 gations of this area, it is that a too faithful reliance 

 on the correspondence between visible brain markings 

 and functional significance in this or any other region 

 in this or any other animal is a trap for the unwary. 



Ferrier's observations apparently satisfied everyone 

 for about 20 years because, for that period of time, no 

 other work appeared, either to contradict or to modify 

 Ferrier's conclusions. In 1899 Larionow (52) defined, 

 also from experiments on cats, remarkably precise 

 (though incorrect) boundaries of an S-shaped strip of 

 cortex coursing along the gyral crest beginning at the 

 middle ectosylvian gyrus, doubling back down the 

 posterior ecto.sylvian gyrus and redoubling around the 

 inferior end of the posterior suprasylvian sulcus for a 

 short distance. Larionow was the first, though not the 

 last, to see in his auditory strip a representation of an 

 'unfurled cochlea', an expression which has proved 

 attractive to several workers through the years. In- 

 deed, though Larionow unrolled his cochlea too far 

 back, there is a note of prophecy and a modest degree 

 of validity to the concept, as later events have shown. 



A year prior to Larionow's report Vogt (104) had 

 pointed otit that the ectosylvian cortex of the carni- 

 vore is an area of early myelination. By the turn of 

 the century, therefore, the feline auditory area had 

 been located, though not precisely defined, by crude 

 functional methods; the same area had been shown 

 to have special histological characteristics and the 

 ideaof cochlear projection had been introduced. Thus, 

 the ideas which were to guide the future study of the 

 cortical auditory area were all present. The subse- 

 quent additions can be thought of as refinements and 

 variants of method, the advent of good electrical 

 recording methods during the 1930's constituting the 

 only radical departure since. Even this has been used 

 without much change in pattern of thinking until very 

 recently. 



There are several ways in which one might trace 

 the development of knowledge of the auditory cortex. 

 In order to show how we have arrived at our present 

 knowledge and attitudes we will here adopt an ap- 

 proach which will be, in the main, sequential, but 



will deviate from strict chronology by first defining 

 certain questions which were or might rea.sonably 

 have been asked at the beginning and considering the 

 successive steps which have been taken toward an- 

 swering these. Thus, departures from strict chronology 

 will be necessary when solutions to questions have 

 been found not in what at the beginning might have 

 tjecn logical sequence. More often than not this has 

 occurred when it was generally thought that, for 

 example, question i had been answered and one might 

 proceed to question 2, only to find in the cour.se of 

 investigation of question 2 that question i had not 

 been answered as fully as it had seemed. 



Given the general location of a functional cortical 

 area, the next question is to determine the extent of 

 the area. This question has been asked at least tacitly 

 in nearly all investigations for over 50 years, even 

 when the stated central question of a particular study 

 was of a more esoteric nature. One reason which 

 makes this determination an almost mandatory start- 

 ing point for any study of the auditory cortex is that, 

 because of individual variation, there are no configur- 

 ative landmarks which can be relied on except in the 

 most general way; therefore, if the experiment pre- 

 supposes exact knowledge of extent of auditory pro- 

 jection, this must be determined for each animal as 

 the starting point. 



The animal most frequently used in experiments on 

 the auditory area is the cat with the monkey (espe- 

 cially macaque) next most frequently; the dog has 

 been used in only a few cases. Unless otherwise 

 specified, the ensuing discussion may be assumed to 

 refer to the cat as the experimental animal. Figure 2 

 shows the standard lateral view of the cat brain which 

 will be used in subsequent figures in portraying the 

 auditory area maps of several studies. 



Vogt's myelination time studies represented the 

 first application of a detailed morphological method 

 of study to the auditory cortex. Campbell (21) in 1905 

 produced the first careful study of the region by the 

 cytoarchitectonic method. Campbell's area is shown 

 in figure 3. (In this figure, the total extent of the 

 cortex considered to be auditory in function is shown 

 in each case. Each portrays the original data as 

 nearly as these could be projected from the original 

 publication to the standard view of the cat brain used 

 in all. Subdivisions are ignored for purposes of the 

 immediate discussion but will be considered in the 

 next section.) It is interesting to note that Campbell's 

 auditory area is the most extensive of any but the 

 latest published and is remarkably similar in some 

 respects to the total composite area which would ex- 



