8 



Survey of Neurobiology 



ciplines provide one another with a num- 

 ber of interesting and provocative prob- 

 lems. It is clear that they can best be 

 solved by the cooperative efforts of neu- 

 rophysiologists and neuroanatomists. There 

 are many other ways in which cooperation 

 between these two subdivisions of neuro- 

 biology may lead to advances. One of these 

 might well be a fresh attack on the prob- 

 lem of the relation of cytoarchitectural 

 fields of the cerebral cortex to functionally 

 defined areas and to the thalamic nuclei. 

 Such an attack could well be carried out 

 by comparing the cortical fields with the 

 sensory areas mapped by the method of 

 evoked potentials. Already studies have 

 been undertaken to determine the thalamic 

 degenerations resulting from precise abla- 

 tions of the several mapped areas. 



In this connection one should draw at- 

 tention to the considerable masses of gray 

 matter which cannot be assigned any spe- 

 cific function. Foremost among these are 

 parts of the so-called rhinencephalon, es- 

 pecially the hippocampal formation and 

 portions of the amygdaloid complex. There 

 is no valid evidence that these structures 

 subserve olfactory functions and there are 

 good reasons for supposing that they are 

 not parts of the "smell brain." Here anato- 

 mical description is far ahead of physiolo- 

 gical analysis. 



7. Comparative Studies. Comparative 

 neurophysiology is a neglected subject. 

 This is a most unfortunate state of affairs, 

 for there are reasons to believe that com- 

 parative studies may yield information that 

 cannot be obtained in any other way. In 

 the evolution of the mammalian series the 

 central nervous system underwent a de- 

 velopment that is far beyond that of any 

 other organ system. The cardiovascular 

 systems of dog and man differ only in minor 

 details. The brains of these two species 

 differ markedly. It is therefore far easier 

 to apply experimental residts obtained on 

 the dog's heart to the problems of cardiol- 

 ogy than it is to use "dog neurology" in the 

 elucidation of the functions of the human 

 brain. When, however, a specific aspect 

 of cerebral organization is studied syste- 

 matically in a series of mammals, say, from 



marsupial to monkey, species differences 

 become less striking, a fairly smooth curve 

 can be plotted and an "extrapolation" to 

 man is likely to yield a good working hy- 

 pothesis. When Woolsey and his collab- 

 orators had mapped the sensory areas of 

 the cortex in a small number of diverse 

 species by the method of recording evoked 

 potentials, they were able to make correct 

 predictions as to the loci of the areas in the 

 brains of intermediate and "higher" forms. 

 At the same time the results established 

 for the first time homologies between the 

 widely differing fissures of the different 

 species. Such results suggest that much 

 of value will be obtained when similar com- 

 parative studies are carried out. 



8. Analysis of Cerebral Mechanisms In- 

 volved in Various Modes of Behavior by 

 the Method of Surgical Ablation. It has 

 been established that many coordinated 

 and patterned acts depend on specific cen- 

 tral mechanisms that lie within sharply 

 bounded portions of the brain. Although 

 destruction of the delimited region perma- 

 nently abolishes all possibility of evoking 

 the total response, some items of the pat- 

 tern may still be elicited. Further, with 

 the essential region intact it is usually easy 

 to show that other parts of the brain exert 

 modifying influences upon it. This can 

 be most readily demonstrated by surgical 

 procedures. The result usually suggests 

 the operation of a series of checks and bal- 

 ances. At this point other techniques might 

 be employed to advantage as has been done 

 in certain instances, notably in the case of 

 the respiratory center. 



In neurophysiology the method of abla- 

 tion is an old one, but it remains useful 

 and it has undergone numerous refine- 

 ments, thanks to the influence of the neu- 

 rosurgeons. It has thrown light on the 

 neural bases of both stereotyped and 

 learned modes of behavior. It appears that 

 it may be useful in analyzing still more 

 complex central mechanisms. In man 

 frontal lobotomies and "topectomies" may 

 produce extraordinary changes when a 

 deep-seated disorder is present. It is not 

 known why these effects are produced. 

 Results already obtained on animals sug- 



