Slow-wave sleep in the TPJ is linked to individual differences in implicit bias

Introduction:
Implicit biases can profoundly impact social interactions and decision-making processes. Here we examine whether the heterogeneity in implicit racial bias can be attributed to interindividual differences in the intracortical distribution of slow-wave activity (SWA), an established key marker of sleep depth.

Material and Methods:
We conducted overnight high-density EEG recordings in the homes of 52 healthy adults (27 females; agemean = 21.5 (SD = 2.0)) during a typical night’s sleep. Implicit racial bias was assessed using the race Implicit Association Test (IAT).

Results:
Whole-brain corrected source localization analysis revealed a significant association between higher SWA current density in the left temporoparietal junction (TPJ) and lower levels of implicit racial bias (p = 0.001, r = -0.45, R2 = 0.20).

Conclusion:
Given the pivotal role of the TPJ in social cognitive processes - such as mentalizing, the process of understanding others’ mental states - we propose that deeper sleep in this region, as indicated by higher SWA current density, might reflect higher inherent mentalizing abilities. In turn, this could lead to reduced implicit racial bias. By using a novel approach to investigate the link between sleep and social functioning, our findings suggest that local aspects of sleep could explain inter-individual differences in social cognition.