Healthy volunteers will be recruited. All subjects will be tested a battery of
neuropsychological tests, then undergo fluorodeoxyglucose-positron emission tomography (PET)
and magnetic resonance imaging (MRI). During the PET and MRI, they will be stimulated with
transcranial direct current stimulation (tDCS) for 15 minutes. Half of subjects will receive
real tDCS and the other half will receive sham tDCS.