A: There are different stage of sleep: light, REM (rapid eye movement) and slow wave -- a deep sleep where the electroencephalograph shows very deep, slow oscillations. There is a lot of evidence that episodic memories -- memories of events -- are consolidated during slow wave. When a memory comes in, it's encoded in the hippocampus, but this is not stable. During slow wave sleep, the memory is transferred to the nearby neocortex, where storage is more stable. Evidence suggests that what is special about deep sleep is that these different brain regions start talking to each other, so memory can be consolidated.

A: We show that the initial session -- before the nap -- does counter the bias, so it's not just that sleep can help with learning or unlearning something unwanted. But the nap greatly strengthened the process. Without it, the change essentially vanished after a week.

A: During sleep, the auditory cue that was originally paired with learning can reactivate the learning and consolidate it. But even without that cue, a memory can be spontaneously reactivated during slow wave sleep; what we learn in the day will be consolidated in the evening. The advantage of our technique is that selecting the cue can select which memory to consolidate. A couple of prior studies used this technique to choose which memory to consolidate, but we were the first to use it to affect social memory, attitudes. The basic pattern, that you can cue memory, was seen before, but what was novel here was the use to affect implicit social bias. And because social bias comes from early experience, it's hard to change

A: This was done in the lab. People may not be able to use this directly in real life, but the principle here is that during sleep, you can reactivate learning that you want to consolidate. We can rehearse something that is important to us. If you think about an important memory and rehearse it before sleep, it's likely to be reactivated during sleep, that's been shown by previous research, and so the basic principle is still the same.

A: We can speculate it would be great while studying to play a sound in the background to create an association between the sound and learning. When you fall asleep, you could play that sound over and over. That may be helpful, but we need more data to know for sure. It might work with other types of unwanted bias, related to disability or sexuality. You could think of fear as a kind of unwanted memory, and there are other studies that have shown a reduction in fear during sleep.

A: Good question. I don't think our study can answer that one way or the other. Maybe it's some of both. By consolidating the new attitude or memory, that creates competition between it and the old attitude, so the old attitude will be weakened.