HUDSON HOAGLAND 
that injection of the stimulant drug after completion of the trial 
improves learning indicates that the drug has affected consoli- 
dation of the learning process directly. The apparent facilita- 
tion of storage of acquired information by the use of drugs, 
as reflected in improved learning, suggests that possibly in the 
future there will be interesting practical applications to the 
learning process. 
What is it that constitutes the chemical change in neurones 
associated with the storage of information? Studies show that 
the ribonucleic acid (RNA) of neurones is markedly increased 
when the neurones conduct impulses and this increase is accom- 
panied by enhanced protein synthesis. The protein so synthe- 
sized in response to activity may represent the memory trace. 
The structure of deoxyribonucleic acid (DNA) molecules in 
the nucleus of egg and sperm is the information code of the 
gene which informs each oncoming generation how to make a 
person. As a template it synthesizes RNA which then produces 
the cell’s proteins, including its enzymes. The hypothesis that 
modifications of neuronal RNA may be the basis of information 
storage in the brain is therefore very attractive since DNA and 
RNA with their highly specific code of arrangements of patterns 
of four linked bases are already known to constitute the blue- 
print for heredity. 
Holger Hydén and his collaborators have developed elegant 
microchemical methods to study individual neurones in different 
parts of the nervous system in relation to their content of RNA 
and proteins before and after they have been involved in con- 
ducting impulses. When tricyano-aminopropine, a dimer of 
malononitrile, is administered to rabbits (20 mg./kg.), after one 
hour it elevates Deiters’ nerve cell protein by 27 per cent, with 
an accompanying increase in this cell’s RNA of 26 per cent. 
Moreover, tricyano-aminopropine changes the relative amounts 
of two of the four bases that constitute by their arrangement in 
the RNA molecule the code of information necessary for specific 
protein synthesis. Of special interest in this connexion was the 
finding that tricyano-aminopropine administered to human 
subjects is followed by an increase in suggestibility. Hydén 
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