Are the broad cognitive improvements seen with tDCS in healthy controls a result of general or specific effects?

INTERVENTION: This is a randomised double‐blind placebo‐controlled within‐subjects design. Participants will receive 20 minutes of either active or sham transcranial direct current stimulation (tDCS). Each participant will attend the Monash Alfred Psychiatry Research Centre on two occasions at least 72 hours apart. Active tDCS will be delivered using electrodes placed within the Starstim system cap. The anode, or activating, electrode will be placed over F3 according to the 10‐20 international system for EEG placement, which has been determined to be an accurate estimate of the left DLPFC. The cathodal, or reference, electrode will be placed over the right supraorbital space. Stimulation will be applied at 0.028 ma/cm for 20mins. Sham tDCS is achieved by switching off stimulation after approx. 30s ; which occurs within the software of the Starstim system allowing for administrator and patient blinding. CONDITION: Cognitive function PRIMARY OUTCOME: The primary outcome measures will be the accuracy and RT measures from the following cognitive task: ; ; b .Speed of information processing task: In this task two different stimuli will appear on a computer screen (either an A or an X). Participants will be required to respond with a button press only when the letter A appears on the screen (duration 5 mins). This task is a measure of attention and processing speed. The primary outcome measures will be the accuracy and RT measures from the following cognitive task: ; a..Reaction time task: This will require participants to respond with a button press when an X appears on the computer screen before them. (duration 5 mins). This task is a measure of attention and processing speed. ; The primary outcome measures will be the accuracy and RT measures from the following cognitive task: ; c..Working memory task: The working memory assessment will consisted of 5 minutes of the 2‐back and 5 minutes of the 3‐back. For the n back tasks a (pseudo‐) random series of the letters A to J are presented consecutively and participants are required to respond with a button press when the presented letter was the same as the letter presented either 2 or 3 trials earlier. (duration 10 mins) SECONDARY OUTCOME: The secondary outcome will be electrophysiological: ; The electrical activity of the brain will be recorded using the StarStim Enobio System (Neurolectrics, Spain). We will use an 8 electrode array and mastoid electrodes will serve as the reference. ; This is the fourth primary outcome measure and includes accuracy and RT measures from the following cognitive task: ; ; d..Social Decision Making task: This task will require participants to answer a series of questions with either YES or No responses via a button box (i.e. Are you in Paris?). They will be instructed for each question to either tell the truth or lie. (duration 5 mins). This task is a measure of executive function. INCLUSION CRITERIA: Inclusion Criteria 1. Are voluntary and competent to consent, 2. Are right handed, 3. Are between the ages of 18 and 45 years, 4. Are native English speakers 5. Have no history of neurological illness, mental illness or traumatic brain injury.