The Song of the Cell: An Exploration of Medicine and the New Human

by Siddhartha Mukherjee

In the 1960s and 1970s, Greengard’s experiments had led him to a novel way of thinking about neuronal communication. Neurobiologists studying the synapse had largely described the communication between neurons to be a rapid process. An electrical impulse arrives at the end of the neuron—i.e., at the axon terminal. It causes the release of chemical neurotransmitters into a specialized space—the synapse. The chemicals, in turn, open channels in the next neuron, and ions surge in, reinitiating the impulse. This is the “electrical” brain—a box of wires and circuits (with a chemical signal—a neurotransmitter—thrown in between the two wires). But Greengard argued that there was a different kind of neurotransmission. The chemical signals sent out by one neuron also create a cascade of “slow” signals in the neuron. Neuronal signaling from one cell to the next instigates profound biochemical and metabolic changes in the recipient cell. An elaborate cascade of chemical changes is sparked off in the recipient neuron: alterations in metabolism, in gene expression, and in the nature and concentration of chemical transmitters that are secreted into the synapse. And these “slow” changes, in turn, alter the electrical conduction of an impulse from nerve to nerve. For decades, this slow cascade was considered peripheral (“Oh, he’ll eventually come around,” another researcher said of Greengard’s work). But the biochemical alterations produced in neuronal cells—the “Greengard cascade”—is now...