Of Mice and Men

How rats and humans are alike;

Rats can learn to crave the same drugs that we do — alcohol, cocaine, nicotine, amphetamine — and they, like us, will sometimes indulge themselves to death. They’re sociable, curious and love to be touched — nicely, that is. If a rat has been trained to associate a certain sound with a mild shock to its tail, and the bell tolls but the shock doesn’t come, the rat will inhale deeply with what can only be called a sigh of relief.

When it comes to sex, the analogies between rats and humans are “profound,” said James G. Pfaus of Concordia University in Montreal. “It’s not simply instinctual for them,” he said. “Rats know what good sex is and what bad sex is. And when they have reason to anticipate great sex, they give you every indication they’re looking forward to it.”

They wiggle and paw at their ears, hop and dart, stop and flash a come-hither look backward. “We imbue our desire with words and meaning, they show us through actions,” he said. “The good thing about rats is, they don’t lie.”

There are more than 120 species of rat in the world, but only two have become serious human pests: the black rat notorious for its role in spreading plague, and the larger brown rat, also called the Norway rat because it was mistakenly thought to have entered Europe through Norway. The Norway rat has largely displaced the black rat as prime urban vermin, and it’s the rat you see in trash cans, parks and on subway platforms. The so-called fancy rats that people keep as pets are variants of the Norway rat, usually albino though sometimes mottled like calico cats, and bred to have docile temperaments.

Scientists began using albino Norway rats for research sometime around the turn of the 19th century, and though the rats have been inbred into homogeneous strains with names like Wistar and Sprague-Dawley, they retain enough street credibility that when a scientist recently released a group of lab rats into a wilderness-type habitat and filmed their reactions, the rodents soon began acting like wild rats. They explored every crevice as rats can do so fluidly, by collapsing their rubbery skeleton down to the width of their snout. They found everything edible in the vicinity, and, though they’d been reared in metal enclosures, they began digging, digging, digging, stopping only to check out the opposite sex and maybe waggle an ear.

Rats have personalities, and they can be glum or cheerful depending on their upbringing and circumstances. One study showed that rats accustomed to good times tend to be optimists, while those reared in unstable conditions become pessimists. Both rats will learn to associate one sound with a good event — a gift of food — and another sound with no food, but when exposed to an ambiguous sound, the optimist will run over expecting to be fed and the pessimist will grumble and skulk away, expecting nothing.

In another recent study, Jonathon D. Crystal, a psychologist at the University of Georgia in Athens, and his colleague Allison Foote were astonished to discover that rats display evidence of metacognition: they know what they know and what they don’t know. Metacognition, a talent previously detected only in primates, is best exemplified by the experience of students scanning the questions on a final exam and having a pretty good sense of what their grade is likely to be. In the Georgia study, rats were asked to show their ability to distinguish between tones lasting about 2 seconds, and sounds of about 8 seconds, by pressing one or another lever. If the rat guessed correctly, it was rewarded with a large meal; if it judged incorrectly, it got nothing.