Diamond is the memory expert with a lousy memory, the one who recently realized, while driving to the mall, that his infant granddaughter was asleep in the back of the car. He remembered only because his wife, sitting beside him, mentioned the baby. He understands what could have happened had he been alone with the child. Almost worse, he understands exactly why.
The human brain, he says, is a magnificent but jury-rigged device in which newer and more sophisticated structures sit atop a junk heap of prototype brains still used by lower species. At the top of the device are the smartest and most nimble parts: the prefrontal cortex, which thinks and analyzes, and the hippocampus, which makes and holds on to our immediate memories. At the bottom is the basal ganglia, nearly identical to the brains of lizards, controlling voluntary but barely conscious actions.