Evidence Against Combined Effects of Stress and Brain Stimulation on Working Memory

Abstract

The effect of stress on working memory has been traced back to a modulation of the prefrontal cortex (PFC). We investigated the effects of neuromodulation of the left dorsolateral prefrontal cortex (lDLPFC) after exposure to psychosocial stress through the Socially Evaluated Cold Pressure Test (SECPT). The hypothesis was that neuromodulation interacts with the stress intervention, to either boost performance even under stressed conditions or compensate negative stress effects. Fifty-nine participants were randomly divided into two groups. One group received active, anodal, offline transcranial direct current stimulation (tDCS) over the lDLPFC while the other group received sham stimulation. Participants performed a lexical n-back task, before and after the SECPT and tDCS intervention. The first n-back task was used as a baseline measurement and the second n-back task was performed during recovery from stress when cortisol levels are at their peak, but still under the influence of tDCS aftereffects. Additionally, after the psychosocial stress phase participants were post-hoc divided into cortisol responders and nonresponders. Results showed that generally stress increased lexical n-back task performance as indicated by faster correct reaction times and higher accuracy but that this was not modulated by tDCS. Crucially, using Bayes analysis we obtained evidence against the influence of anodal tDCS on stressed individual’s working memory performance.

Keywords

• transcranial direct current stimulation
• stress
• cortisol
• working memory
• nback