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Diamond says that in situations involving familiar, routine motor skills, the human animal presses the basal ganglia into service as a sort of auxiliary autopilot. When our prefrontal cortex and hippocampus are planning our day on the way to work, the ignorant but efficient basal ganglia is operating the car; that's why you'll sometimes find yourself having driven from point A to point B without a clear recollection of the route you took, the turns you made or the scenery you saw.

Ordinarily, says Diamond, this delegation of duty "works beautifully, like a symphony. But sometimes, it turns into the '1812 Overture.' The cannons take over and overwhelm."

By experimentally exposing rats to the presence of cats, and then recording electrochemical changes in the rodents' brains, Diamond has found that stress -- either sudden or chronic -- can weaken the brain's higher-functioning centers, making them more susceptible to bullying from the basal ganglia. He's seen the same sort of thing play out in cases he's followed involving infant deaths in cars.

"The quality of prior parental care seems to be irrelevant," he said. "The important factors that keep showing up involve a combination of stress, emotion, lack of sleep and change in routine, where the basal ganglia is trying to do what it's supposed to do, and the conscious mind is too weakened to resist. What happens is that the memory circuits in a vulnerable hippocampus literally get overwritten, like with a computer program. Unless the memory circuit is rebooted -- such as if the child cries, or, you know, if the wife mentions the child in the back -- it can entirely disappear."