Failure of tDCS to impact militarised threat-detection in a military cohort.

Transcranial direct current stimulation (tDCS), a form of non-invasive brain stimulation, has become a focus of military organisations due to its reported positive effects on cognitive and motor performance. However, the majority of tDCS research in this space is conducted with civilian participants and/or uses abstract tasks. Additionally, of the small subset of studies that have used military participants or military-relevant tasks, few have employed both, and none with a considerable sample size. Here, we extend on previous work by exploring whether tDCS to the right inferior frontal gyrus (rIFG) enhances the performance of a large military cohort during a militaristic threat-detection task. 98 participants aged between 18 and 45 were randomly assigned to one of three conditions: (1) 2 mA anodal tDCS to the rIFG; (2) Sham stimulation to the rIFG; or (3) 2 mA anodal tDCS to the visual cortex (V1). Participants viewed serially presented, virtually generated militaristic images, and responded Yes/No via keypress to a threat being present. tDCS was applied for 25 min during the first two training blocks of the 50 min task. Results showed evidence for the null hypothesis: tDCS did not influence mean accuracy or reaction time across the task, in contrast to previous work. We discuss possible methodological and population factors that may explain why previously published effects of tDCS were not reproduced.