DISTURBANCES OF NEURAL FUNCTION IN THE PRESENCE OF CONGENITAL DISORDERS 



!9 r 3 



that muscle and this enables it to make connections 

 with central coordination centers appropriate for 

 the function of that muscle only. That this really 

 happens is demonstrated by experimentally making a 

 nerve developing from the trunk, for example, grow 

 into a forelimb. The nerve acquires the 'sign' of the 

 limb muscles which somehow enables it to make con- 

 nections with the coordination centers for the limb 

 rather than the trunk from which it began. Each fiber 

 from the retina becomes specific for the particular 

 geographical part of the eye in which it originates, 

 and sensory nerve fibers growing into the skin acquire 

 a property that identifies them with a particular zone 

 of the skin and no other. In the adult the specific 

 quality of the nerve fibers has become incorrigible. 

 In man this is well exemplified by the failure of a hypo- 

 glossal nerve, anastomosed to the distal part of a cut 

 facial nerve, ever to take over the functions <>l .1 facial 

 nerve. Numerous other examples of this self-deter- 

 mination process during the development of the 

 nervous system involving the motor, sensory and 

 special sense circuits may be found in Weiss ( 35 

 36), Sperry (29, 30) and Stone (31). Altogether de- 

 velopment is an inexorable business that follows 

 along lines determined by the genetic endowment of 

 the organism. The nervous system, to be sure, is an 

 adaptive and adjusting mechanism (23), but the 

 machinery for the mechanism is laid down in a man- 

 ner predetermined by the ontogenetic processes 



With this brief reference to neural development 

 we can pass on to descriptions of representative ab- 

 normalities. They will be grouped rather arbitrarily, 

 for the separation of anatomic from biochemical 

 disorders and late from early disturbances is often 

 artificial. In each group, reference will be made to a 

 number of examples (when there are a number) and 

 one or two will then be considered in more detail. 



ANATOMIC ABNORMALITIES 



Structural abnormalities of the nervous system 

 that can be seen grossly or microscopically are in- 

 numerable in man (7) and in some other mammals 

 (17). While the majority represent mutants and 

 phenocopies in the sense outlined earlier, certain 

 forms of trauma and asphyxia in the perinatal period 

 in man can produce serious anatomic injuries that 

 do not fall into the 'genetic' categories. The disturb- 

 ances of function that go with this variety of anatomic 

 disorders are as diverse as the structural patterns of 

 damage that may result. Since the factors concerned 



the kind of trauma, the asphyxia, hemorrhage and 

 ischemia — are so variable and often combined, there 

 is no specific pattern of injury. Of the patterns of 

 grossly evident malformation that have their origin 

 earlier in development than the perinatal period 

 there are myriads. Diminutions in the gross size and 

 convolutions of the cortex (microcephalies), and 

 structural defects of the basal ganglia, corpus cal- 

 losum, parts of the cerebellum and the brain stem 

 are examples of the broad categories that can be seen. 

 In general the disturbed function is directlv referable 

 to the defects. A relative lack of the lateral thora- 

 columbar (sympathetic) spinal cord s;ray columns or 

 a discrepancy in the number of myenteric neural 

 plexuses in the colon itself may lead to a pathologically 

 distended colon (megacolon). Abnormalities of the 

 cytoarchitecture of the cerebral cortex, basal ganglia 

 and brain-stem nuclei at the microscopic level are 

 numerous in variet) and max be associated with 

 degrees of mental retardation, behavior disorders or 

 motor abnormalities 



A considerable number of developmental abnor- 

 malities express themselves in young adult life or even 

 in old age. They too appear as structural abnormali- 

 ties but the) also illustrate how hard it is to cate- 

 gorize them as 'anatomic,' 'biochemical, 1 etc. Some 

 will be mentioned in another section. 



1 1 1 / holy 



This is a not uncommon abnormality in man that 

 illustrates anatomic deformity in just about its most 

 severe form, h has been known at least since early 

 Egyptian times (27), for the mummy of such an 

 infant was found in a tomb for sacred animals. It 

 was apparently believed by the Egyptians that the 

 sire of the child must have been a monkey. The 

 condition is characterized by severe gross deficit of 

 the brain and upper spinal cord ranging from what 

 is described as complete absence of brain to an open 

 plate of neural tissue capable of some functional 

 activity. Usually two bulging froglike eyes are present, 

 cyclopia being a rare accompaniment. Most such 

 infants or fetuses are females and the most likely 

 background for the condition is that it represents a 

 homozygous recessive genetic situation with variable 

 expression. One judges that the deviation from 

 normal developmental paths must first become evi- 

 dent at the time that the mesoderm is first inducing 

 the nervous system, although by analogs' with mon- 

 sters in other animals it is puzzling why the eyes 

 should be so well-developed. Possibly the involve- 



