Reducing attention bias toward negative emotional stimuli with transcranial random noise stimulation: a randomized, double-blind, sham-controlled, crossover study

Excessive attention bias interferes with daily life and contributes to various psychiatric conditions. Previous studies have demonstrated that anodal transcranial direct current stimulation (tDCS) applied to the left dorsolateral prefrontal cortex (DLPFC) can enhance attentional control and reduce negative emotional bias. However, little is known about the effects of transcranial random noise stimulation (tRNS) on attention bias. This study aimed to investigate whether tRNS reduces attention bias toward negative emotional stimuli compared to tDCS, for which functional evidence has been established. This randomized, double-blind, crossover, sham-controlled study enrolled 32 healthy right-handed men. The emotional Stroop task was used to assess attention bias. The participants experienced all three stimulation conditions: tRNS, tDCS, or sham, with each condition separated by a 7-day washout interval and administered in a random order. tRNS to the left DLPFC significantly reduced attention bias toward negative stimuli compared with sham (corrected p = 0.047, Cohen’s d = 0.72), whereas no significant difference was observed between tRNS and tDCS. Positive correlations were observed between the effects of each stimulation condition and attention bias in the sham condition in the tRNS and tDCS groups; however, these associations did not exceed the empirical null distribution determined by permutation testing. Thus, the modulatory effects of tRNS on attentional control may not strictly depend on baseline bias magnitude, suggesting its potential applicability in both healthy and clinical populations characterized by excessive attention bias. Clinical Trial Registration: This study was registered in the University Hospital Medical Information Network Clinical Trial Registry in Japan (UMIN000052202) on 09/13/2023; https://center6.umin.ac.jp/cgi-open-bin/ctr_e/ctr_his_list.cgi?recptno=R000059574.