Transcranial Direct Current Stimulation (tDCS) and Cognitive Processing

Participants enrolled into this study may be asked to do the following: * Grant permission for the researchers to view medical records associated with their language/cognitive difficulties (if applicable. * Complete a questionnaire, provide a health history, and take some pencil-and-paper tests of problem-solving and memory in order to verify eligibility to participate and to able to safely undergo the experimental procedures. * Complete several tasks (i.e., saying words out loud, naming objects, drawing designs, remembering lists of words, searching for images or letters, and/or completing puzzles) based upon a number of cognitive functions such as language, memory, vision, processing, and perception. * Wear electrodes that will be placed on the scalp with a large rubberized band. These electrodes will administer very weak electrical current (tDCS) from a battery powered device for 20 to 60 minutes. * Participation in several study conditions. The exact conditions and their order will be randomized. Under some conditions, participants may receive active stimulation (tDCS) and under other conditions, they may receive sham stimulation. * The experimental sessions will last approximately 2 hours and participants may be asked to have more than one testing session in a day or to return for additional sessions. * Have a Magnetic Resonance Imaging (MRI) brain scan.