No matter how open-minded you think you are, you're chock-full of what scientists call implicit biases -- prejudices you don't even realize that you have that color your actions. But a fascinating new study suggests that these biases can be cut down in your sleep. By having subjects go through a bias-diminishing exercise just before taking a nap -- during which the things they'd just learned were cued up by special sounds -- researchers were able to lower their biases up to a week after the fact. The results were published Thursday in Science.

Xiaoqing Hu, lead author of the study and a postdoctoral researcher at the University of Texas at Austin, was working on ways to diminish implicit biases, like unconscious feelings of racism and sexism, when he happened to read an article on sleep research. Other scientists were finding evidence that sleep could help solidify and strengthen memories.

Would it work, he wondered, to insert the "memory" of a broken bias?

After testing implicit biases against black people and women using a standard experiment (which tests how closely words with positive and negative connotations are unconsciously linked to members of a particular group), Hu and his colleagues ran a procedure meant to reverse those biases. During this activity, the 40 subjects -- male and female college students -- were asked specifically to make face and word pairings that went against implicit biases: They were told to match female faces to words associated with the sciences and math, not art, and to match black faces with positive words.

This is a common trick for reversing bias, and it worked. But what happened next was much cooler.

Every time one of those test subjects clicked an association that reversed bias (pairing a female face with a science word, for example) a particular tone sounded in the background. There was a different tone for making a pairing that fought implicit racial bias.

After their testing, the subjects were asked to take a 90-minute nap. Meanwhile, some of them were cued with one of the two tones they'd heard during the experiment. The idea here is that the sound primes the brain to focus on the memory of playing the game, giving anything learned during the session a boost.

Sure enough, the subjects who heard tone cues during their naps showed a 50 percent reduction in their baseline bias after waking up.

And a week later, when subjects who hadn't heard tone cues had slid back to their baseline level of bias, those who'd heard the tones in their sleep maintained something like a 20 percent reduction.

"What we think is happening is that the new memory, which is very weak, is stored in the hippocampus," Hu said. "But when it's activated by this sound cue, perhaps it's reorganized into the neocortex, where memories are more stable and longer lasting."

Hu isn't surprised that the bias reduction was almost gone after a week. "We're doing a single shot," he said, "and a short nap. And then they went back to their normal lives, where all of the original biases and stereotypes they saw before in peers and in the mass media returned."

But given that other subjects dropped back to their baseline, he's excited that the cued subjects had any bias reduction at all. They'll have to do more research to see if they can make the effect last longer than a week, but there's indication that it might: The subjects who went into deeper, higher-quality sleep in the lab had a better bias reduction a week later than those who napped lightly. Hu is looking forward to using a full night's sleep as the memory-booster.

Memory and sleep specialist Jan Born of the University of Tuebingen (who wasn't involved in the new study) agreed that there was more work left to do before the findings could make their way out of the lab, but found the results promising.

"This study shows that targeted memory reactivation can be used to 'implant' new memories that counter very deeply rooted memories of implicit attitudes," Born said."This is an impressive novel finding, although as a sleep researcher working in the same field of sleep-dependent memory formation I personally was not too surprised. This study shows how extremely powerful memory formation during sleep can be."

And Born expects people to try to tap into that as soon as scientists get a handle on how it works.

"Sooner or later, “targeted memory reactivation” will be a method that, perhaps combined with a smart phone app, will enter our everyday life," he said.

When that day comes, according to Hu, the implications could be pretty far reaching. Racism isn't the only habit people could try to break in their sleep.

"We think of it as learning a new habit -- learning a new one to cut back on our old, unwanted one," he said. "So if this can happen to the prejudice habit, then maybe it could be used for things like smoking and overeating."

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