Noninvasive brain stimulation reduces prejudice scores on an implicit association test

Inhibiting the anterior temporal lobe (ATL) via repetitive transcranial magnetic stimulation (rTMS) appears to have deleterious effects on people's semantic conceptualization, and left ATL damage is associated with semantic dementia. However, little research has investigated whether rTMS can inhibit conceptual schemata that have potentially negative consequences. Our aim was to investigate whether rTMS to the ATLs could reduce scores on a standard measure of prejudice (implicit association test, IAT).

Forty (17 female; mean age 20.6) neurologically normal, right-handed undergraduates participated. Participants were randomly allocated into one of four rTMS stimulation conditions-left ATL, right ATL, control site (motor cortex, Cz), and sham stimulation. All participants completed a modified IAT, where "good" and "bad" words were replaced with "terrorist" and "law-abider" words, and, "Black" and "White" were replaced with "Arab" and "Non-Arab" words. Participants were then given 15 min of rTMS stimulation. Afterward, participants completed a parallel form of the IAT.

To investigate the effects of rTMS on IAT scores, a one-way ANOVA on the difference between pre- and postscores was carried out revealing that there were significant between group differences (F3,36 = 3.57; p = .02). Planned contrasts revealed that both left and right ATL stimulation significantly reduced IAT scores poststimulation, indicating lower prejudice.

We show that prejudice scores can be significantly reduced by inhibitory rTMS delivered to the bilateral ATLs. This may implicate this area in conceptual associations that lead to overgeneralization and stereotyping of social groups.