Evidence in the literature suggests stimulation to left dorsolateral prefrontal cortex (DLPFC) improves both working and declarative memory in non-patient and patient populations. However, it is not clear from the literature 1) for which patient populations tDCS is effective, 2) for how long tDCS is effective following treatment of varying duration. For this testing a sensitive assessment instrument of cognitive function is necessary. The research team will test the tablet version of the BCoS for its ability to assess the effects of tDCS as described above. A Cantonese version of the BCoS has been developed in the Guangzhou No. 1 Hospital in a previous project and shown to be sensitive to cognitive deficits in populations experiencing stroke, traumatic brain injury, tumour, and dementia. Here the team will measure its ability to assess working memory changes (n-back task; change detection task) and modify as necessary to achieve this aim.