Transcranial Direct Current Stimulation (tDCS) and Cognitive Processing

This research is being done to determine whether transcranial direct current stimulation (tDCS) can improve certain mental abilities. In this research, battery powered device is used to deliver very weak electrical current to the surface of the scalp while participants complete cognitive tasks. Our aim is to find out whether tDCS will improve task performance in both healthy adults and those with neurological impairment.

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.

Eligibility Criteria:
Eligibility Criteria by Study Group

Normal Controls Inclusion Criteria:

* Right handed (as determined by the Edinburgh battery)
* English as native language

Normal Controls Exclusion Criteria:

* Appreciable deficits in hearing
* Appreciable problems with articulation
* Schizophrenia, bipolar disorder, or major depression
* Appreciable accent
* Any neurological disorder associated with cognitive impairment or neuroanatomic abnormality
* Language-based learning disorder
* Any implanted metal device (precludes use of tDCS)
* Any implanted cardiac pacemaker
* Dementia or Mini-Mental State Exam \< 24
* Estimated verbal intelligence \< 70

Aphasia Group Inclusion Criteria:

* Right handed (as determined by the Edinburgh battery)
* English as native language
* History of acquired left-hemisphere dysfunction

Aphasia Group Exclusion Criteria:

* Appreciable deficits in hearing
* Schizophrenia, bipolar disorder, or major depression
* Appreciable accent
* Language-based learning disorder
* Any implanted metal device
* Any implanted cardiac pacemaker
* Mini-Mental State Exam \< 21/27 (omitting naming \& items)
* Estimated verbal intelligence \< 70

Schizophrenia/First-degree Family Members Inclusion Criteria:

* Right handed (as determined by the Edinburgh battery)
* English as native language
* Diagnosis of schizophrenia (SZ) or bipolar disorder (BD)
* First degree family member of individual with SZ or BD

Schizophrenia/First-degree Family Members Exclusion Criteria:

* Appreciable deficits in hearing
* Appreciable accent
* Any implanted metal device (precludes use of tDCS)
* Any implanted cardiac pacemaker
* Dementia or Mini-Mental State Exam \< 24
* Estimated verbal intelligence \< 70

High-functioning Autism Inclusion Criteria:

* Right handed (as determined by the Edinburgh battery)
* English as native language
* Diagnosis of High-functioning autism (i.e., Asperger's)

High-functioning Autism Exclusion Criteria:

* Appreciable deficits in hearing
* Schizophrenia, bipolar disorder, or major depression
* Appreciable accent
* Any implanted metal device
* Any implanted cardiac pacemaker
* Dementia or Mini-Mental State Exam \< 24
* Estimated verbal intelligence \< 70