The effects of trans-cranial direct current stimulation intervention on fear: A systematic review of literature

Intensifying fear and fear of pain may lead to some diseases such as panic disorder, phobias, post-traumatic stress disorder (PTSD), anxiety disorders, depression, etc. A number of studies indicated positive effect of transcranial direct current stimulation (tDCS) on controlling fear and some studies did not observe any effect or even negative effect on decreasing fear. Due to lack of consensus in the findings of research, we aimed to systematically review studies, which investigated the effect of tDCS on fear. A literature search was conducted using the databases of PubMed, Science Direct, OVID, CINAHL, PEDro, Cochrane, Scopus and MEDLINE. Fear, fear memory, fear of pain, anxiety, post-traumatic stress disorder, electrical brain stimulation were applied as keywords. The valid assessment scale was used to evaluate the methodological quality of the included studies. The results of this systematic review revealed that the cathodal tDCS (c-tDCS) on the left dorsolateral prefrontal cortex (DLPFC) as compared to anodal tDCS (a-tDCS) could significantly reduce fear and modulate the fear memory. In addition, the findings of this study showed that the c-tDCS has positive effect on behavioural parameters of fear, while it cannot change biochemical parameters of fear during limited sessions of intervention. Application of c-tDCS on the left DLPFC could significantly reduce fear and modulate the fear memory.