'944 



HANDBOOK HI PHYSIOLOCY 



NEl'ROI'IIYSUlLOGY III 



produce in detail the vastly organized nervous 

 system and tin- whole body. [Indeed, when the two 

 halves of a cat cerebrum are functionally separated 

 bv operation, Sperrv (268) found them to be more 

 i u.i 1 1\ alike in learning ability than are the brains of 

 two different cats, much as identical twins have like 

 intelligence quotients.] Similarly, the equation for 

 calculating pi can produce as many hundreds or 

 thousands oi detailed digits .is one cares to grind out 

 of it. There may well be many interdependent sets of 

 rules in the nervous system for handling; information 

 which we have not yet learned, so that the number 

 of details stored as such, and the attendant storage 

 capacity, may be far less than is currently assumed. 



Besides the inborn information, all developing 

 nervous systems undergo further molding and fixation 

 which, under the constant environment of early 

 embryonic stages, is practically universal to the 

 species. Pieces of the young neuraxis can be rotated or 

 turned end for end or displaced longitudinally, and 

 yet reach normal form in the new- locus and establish 

 appropriate connections (55). Small nerve roots can 

 be led 10 large peripheries or large ones into small 

 peripheries, during embryonic development, and 

 will re-establish an appropriate quantitative adjust- 

 ment of size of nerves and number of libers (291). 

 Peripheral connections, both sensory and motor, can 

 be tangled operativcly, yet the central functional 

 patterns re-form to give normal integrated behavior 

 (jt>H). Some microspecification of the neurons and 

 junctions is thus indicated, much as for the later 

 processes of individual learning and the accompanying 

 formation of memory traces 



In both cases, also, actual growth of some sort is 

 further indicated, a function that may fall ofT with 

 time, rapidly at hist and then slowly, perhaps along a 

 decaying exponential curve. In any event, inodili- 

 abilitv of the nervous swem is extreme in the very 

 early stages when major operative insults cm lie 

 corrected, decreases rapidly until birth when major 

 patterns are irreversibly established and even ana- 

 tomical regeneration is circumscribed, and then more 

 slowlv throughout youth and old age when learning 

 and let. lining new patterns becomes ever more 



difficult and ultimately practically impossible. 



iniiividi vi expi rieni i . Yet much important pattern 

 formation still occurs in infancy .mil youth, and is, 

 ol course, ever more determined by individual rather 

 1I1. in bv universal experience Something like im- 

 printing m. iv well OCCUr in man as well .i^ in ducks; 

 ■ ' 1 Minlv such attitudes .0 fear of sn.ikes and shame 



at nakedness are inculcated early and indelibly. 



[J. G. Miller (personal communication) observed a 

 woman in deep coma, lacking optokinetic reflexes 

 and with bilateral Babinski reflexes, who pulled 

 down her skirt when exposed for examination.] 

 Avoidance conditioned reflexes may extinguish only 

 after autonomic nerve section (-'1)7). Conditioned 

 visceral reflexes to pain or fear or disgust, in dog and 

 man alike, can be established early and endure 

 through life (76, 178). The Australian aborigine, 

 condemned by the tribe for some transgression to have 

 the 'bone pointed' at him, retires and dies on such a 

 basis. The infant chimpanzee or human, raised for 

 the first lew weeks or months of life in the absence of 

 pattern vision, can never develop this properly. 

 Although the eye may later be available as a normal 

 optical instrument, the nervous system has apparently 

 'set' too far for the missing architectural patterns to 

 be established then by the same functional activity 

 that would earlier have succeeded in doing so (245). 

 An especially dramatic example of the importance of 

 experience in laving down material patterns, and one 

 showing as well the importance of pre-existing 

 patterns on which new ones can build again much 

 as the molecular template for macromolecule re- 

 production — is afforded by the removal of one 

 occipital lobe of a rat, followed in 2 weeks bv the 

 removal of the other (207). Before either operation, 

 pattern vision is normal; after the second, it remains 

 present if the animal were allowed normal visual 

 experience during the interval between operations; 

 it is absent if this experience was prevented. 



On the positive side, inolor skills are more nearly 

 perfect when learned in early life, the athlete or the 

 musician who rises to the top has begun training al- 

 most in infancy. Only one's native language, or 

 others learned early, is spoken without an accent; 

 foreign adults cannot usually master the English 



"th" or the French 'r. 1 Trigger points, set up experi- 

 mentally or by accidental trauma, may endure lor 

 life [see Gerard (101 |], as a lingering error made early 

 in learning a composition mav dog a musician's 

 performance ever after. Similarly, if some cerebellar 

 efferent connections to spinal neurons are severed 

 even a lew hours before others, .m enduring posiural 



asymmetry may be established in the spinal cool 

 (Brookhart) as, indeed, the order of removal of the 

 tight and left cerebral 1 01 lex determines the direction 

 of circling. Even the menial and perceptual abilities 

 and the more general intelligence quotient un- 

 doubtedly contain, besides inborn capacity levels, 

 considerable components depending on individual 



