 Transcranial direct current stimulation tDCS is a non-invasive form of brain stimulation which uses a very weak constant current to temporarily excite the brain area of interest via small electrodes placed on the scalp. Currently, tDCS is being used as a tool to investigate mental processes cognition and motor function movement in healthy controls and to treat neurological i.e. stroke and psychiatric i.e. depression and dementia patients. tDCS has been found to improve motor processes and cognitive performance, including attention and memory functions. This study will attempt to examine the effects of tDCS on a specific aspect of short term memory to sounds measured from electrical activity EEG from the top of the scalp. This study will also assess the effect of a drug, dextromethorphan DMO, commonly found in cough syrup, which is thought to regulate tDCS treatment through brain receptors. The study involves four laboratory test sessions. EEG assessments will be done in two sessions involving anodal tDCS stimulation to temporarily excite cortical activity locally, one session with DMO treatment and one with placebo treatment, and two sessions involving sham tDCS stimulation device is turned off, with the same DMO and placebo treatments. These findings will contribute to our understanding of the brain chemistry involved in tDCS treatment and its effects on cognitive abilities. 