VOL. 4 (1950) 



FUNCTIONAL ORGANIZATION OF THE BRAIN 



123 



were similar. At birth the medulla oblongata revealed the highest glycolysis. In the 

 adult, however, it is the cortex that shares the most rapid metabolic rate with the caudate 

 nucleus. 



The developmental progression observed in oxidation and glycolysis has also been 

 found in the distribution of cerebral glycogen. Chemical determinations demonstrate 

 that glycogen concentrations of the cerebral cortex and caudate nucleus increase with 

 age. The percentage of glycogen in the lower parts, however, the cerebellum, medulla 

 and spinal cord diminish progressively and are least in the adult^^. 



The quantitative analyses presented above show that both aerobic and anaerobic 

 mechanisms are accelerated after birth. It seems probable that the more rapid rates 

 are an expression of an increased concentration of enzymes. Such an increase can be 

 accounted for by the growing capac- 

 ities of phosphorylase, phospho- 

 glucomutase^^, adenosine triphos- 

 phatase^ and the cytochrome-cyto- 

 chrome oxidase system^"' ^ occur- 

 ring in the brain during the early 

 postnatal growth of the rat. Carbonic 

 anhydrase though not found in the 

 fetal rat is present in the adult where 

 it is more plentiful in the function- 

 ally dominant cerebral areas than 

 in the cord^^. A study of fetal sheep 

 proved that the enzyme cholin- 

 esterase is present in greater concen- 

 tration in the spinal cord than the 

 brain during early gestation. This 

 relationship however is reversed in 

 the last weeks before birth as the 

 cholinesterase activities of the cord 

 diminish while those of the brain far 

 outstrip it***. This enzymatic evolu- 

 tion which appears earlier in the 

 sheep than in the rat is not to be 

 attributed solely to a difference in 

 the enzyme studied in these two 



species but it must also be remembered that the sheep is further advanced in the 

 development of behavioural patterns at the time of birth. 



To summarize, the increase in metabolic intensity does not occur in all parts of 

 the brain simultaneously, but appears in the various portions at different times. The 

 order of appearance is not a haphazard one but develops first in the posterior portions 

 of the neuraxis and then progresses in an anterior direction. Such a stepwise passage 

 advancing from the older to the newer parts of the brain recapitulates its phyletic 

 development. Since many of the metabolic studies reviewed were made on newborns. 

 It would seem that Haeckel's dictum that ontogeny recapitulates phylogeny^^ should 

 be broadened, in the case of the brain, and the time extended to include early postnatal 

 growth with prenatal development. 

 References p. 125. 



5 6 7 

 Age in wfeks 



Adu'J 



Fig. 3. Oxygen consumption vs. Age Dog Brain Parts. 

 In the first week of life the highest rate of metabolism 

 in the puppy's brain is found in the meduUa; during 

 the third week the midbrain assumes the highest 

 oxj'gen consumption. From the fifth to the seventh 

 week, the respiratory metabolism of all parts, with 

 the exception of the medulla, is higher than the cor- 

 responding values for the first week of life and the 

 caudate nucleus has advanced to the greatest oxygen 

 intake up to this time. In the adult dog the latter still 

 retains its prime position, while the cerebral cortex 

 ascends to second place. The cerebellum, thalamus, 

 midbrain and medulla follow in descending order. 



