SMITH C E
Science. 1962 Nov 23;138(3543):889-90. doi: 10.1126/science.138.3543.889.
Variations in cholinesterase and RNA concentrations and in levels of neural activity have been linked to learning. These three groups of experimental evidence suggest that the basis of memory lies in an increase of the concentrations of enzymes associated with transmitter substances, as a long-lasting effect of stimulation. Biological precedent exists in microbial physiology.