I continue to explore the science in which I work almost like a child, with naïve joy, curiosity, and amazement. - Eric Kandel

Jacob and Monod not only outlined a theory of gene regulation, they also discovered the first regulators of gene transcription. These regulators come in two forms—repressors, genes that encode the regulatory proteins that shut genes off, and as later work showed, activators, genes that encode the regulatory proteins that turn genes on.

What is learning but a set of sensory signals from the environment, with different forms of learning resulting from different types or patterns of sensory signals?

Even though I had long been taught that the genes of the brain are the governors of behavior, the absolute masters of our fate, our work showed that, in the brain as in bacteria, genes are also servants of the environment. ...An environmental stimulus... activates modulatory interneurons that release serotonin. The serotonin acts on the sensory neuron to increase cyclic AMP and to cause protein kinase A and MAP kinase to move to the nucleus and activate CREB. The activation of CREB, in turn, leads to the expression of genes that changes the function and the structure of the cell.