Smart, Curious, Ticklish. Rats?

Between reading recent news reports about altruistic behavior in rats and watching the slickly adorable antics of Remy the culinary rodent in this summer’s animated blockbuster, “Ratatouille,” I’ve had a change of heart. My normal feeling of extreme revulsion toward rats has softened considerably, into something resembling ... a less extreme form of revulsion.

O.K., I still don’t like rats, and I’ll never forget the sensation of whiskers brushing my ankles when a rat in Central Park scampered over my feet. There are plenty of reasons to fear rats. They carry diseases like typhus, leptospirosis, hanta virus pulmonary syndrome, rat bite fever, salmonella poisoning, and of course bubonic plague, and they are ravenous Remys every one of them, feasting on our grains and meats, chewing our ratatouille and destroying as much as a third of global food supplies each year. “Over the past century alone,” writes Robert Sullivan in “Rats,” his magisterial history of the urban pest, “rats have been responsible for the death of more than 10 million people.”

Yet our ratly transactions are not all woes and buboes. As the first mammals domesticated strictly for research purposes, scientists say, rats in the laboratory may well have saved at least as many human lives through the years as rats in the alley have taken. Rats are the preferred experimental animal for studies of the heart, kidneys, immune system, reproductive system, nervous system and other body sectors, and recent breakthroughs in manipulating the rat genome may soon allow the rat to displace the mouse as the geneticist’s darling, too.

And though rats have yet to produce an Albert Camus or design a better mouse trap, a host of new behavioral studies makes plain that the similarities between us and Rattus extend far beyond gross anatomy. They’re surprisingly self-aware. They laugh when tickled, especially when they’re young, and they have ticklish spots; tickle the nape of a rat pup’s neck and it will squeal ultrasonically in a soundgram pattern like that of a human giggle. Rats dream as we dream, in epic narratives of navigation and thwarted efforts at escape: When scientists at the Massachusetts Institute of Technology tracked the neuronal activity of rats in REM sleep, the researchers saw the same firing patterns they had seen in wakeful rats wending their way through those notorious rat mazes.

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.

For each trial, the rat could, after hearing the tone, opt to either take the test and press the short or long lever, or poke its nose through a side of the chamber designated the, “I don’t know” option, at which point it would get a tiny snack. During the trials, the rats made clear they knew their audio limits. The closer the tones were to either 2 or 8 seconds, the likelier the rats were to express confidence in their judgment by indicating they wanted to take the lever test and earn their full-course dinner. But as the tones edged into the ambiguous realms of 4 seconds, the rats began opting ever more often for modest but reliable morsels of the clueless option.

Rats do not lie, and, when the stakes are this high, neither do they gamble.

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