Long-held social biases, such as race and gender prejudices, can be reduced during sleep, suggests a study published in Science.

This study adds further support to recent research that has shown that memories can be selectively reactivated and strengthened during slumber. Scientists have known that sleep boosts memory formation by resuscitating faint neuron activity shaped during earlier periods, when an individual was awake. This process can be experimentally stimulated by giving a sleeping individual cues related to an earlier period of learning.

Now, Xiaoqing Hu and colleagues extend these findings to show that this method not only works for recently learned information but also to influence implicit attitudes learned during childhood.


Illustration credit: P. Huey/Science

In a series of exercises designed to counter typical racial and gender biases, participants were shown pictures of men and women of different races. They learned to associate races and genders with opposing features to what they believed, for example, female faces with science-related words and black men with “good” words. A distinctive sound was associated with each type of counter-bias.

The participants then took a 90-minute nap during which one sound, by random assignment, was repeatedly played to cue and reactivate a newly learned association. Shortly after waking, and again one week later, the researchers found that implicit social biases were reduced preferentially for the counter-bias training reactivated during sleep. (The biases were not reduced for counter-biases not reactivated.)

Given the implications of this research for societal change, Gordon Feld and Jan Born say in a related perspective, the study should inspire research to solve remaining issues of targeted memory reactivation during sleep so that its mechanisms are fully understood.