 The current available treatments for PTSD are not fully effective for cognitive symptoms of PTSD and have high drop-out and poor engagement, two factors found to be most indicative of overall return to functioning for patients with PTSD. Successful completion of this pilot clinical trial may build a platform for future large scale double-blind, placebo-controlled studies using either atomoxetine or psycho-stimulants or other cognitive enhancing medications. The response inhibition related measurements are sensitive to psychotropic medications. Therefore it is advantageous for us to use GNG and Stop Signal approaches to investigate individual treatments response in the investigators future research. The investigators believe GNG and Stop signal approaches together with pharmacogenetic approach will provide valuable information to direct future individualized medicine. 