Cognitive Stimulation Study

The research team conducting the research procedures will perform several tests.
Investigators will ask participants if participants are right or left handed, how far
participants went in school, their job, and a medical history including brain and nervous
system disorders, psychiatric disorders, heart related disorders, and other significant
disorders. Investigators will ask participants for their current medications. Investigators
will ask participants about their history of cognitive function. If participants are a woman
of child bearing potential, Investigators will perform a pregnancy test and the result must
be negative to receive stimulation. Prior to stimulation, Investigators will have
participants complete pre-stimulation computerized cognitive tests involving tasks where
participants are asked to respond to images or sounds presented by a computer. Investigators
will also collect measures of physiological function during the testing session, specifically
heart rate, blood pressure, skin conductance, respiration rate, and pupillary response. These
will be measured using recording electrodes attached to the fingertip, arm, and chest and a
respiration band around the chest. A small camera will record changes in their pupil size.
Investigators will also collect measures of brain structure and function using magnetic
resonance imaging. Investigators will also ask participants to fill out a questionnaire
describing their experience during each study session.

If participants decide to take part in this study, participants will be asked to participate
in up to four different testing sessions separated by at least 24 hours. In each of these
testing sessions, participants will be asked to receive either electrical stimulation or
placebo stimulation during different testing sessions. Placebo stimulation looks like and is
performed in the same way as electrical stimulation, but stimulation is stopped before it can
have an effect. Placebo stimulation is used in research studies to show what effect a
treatment has compared with receiving a lower level of stimulation or nothing at all. Studies
have shown, however, that about 1 in 3 persons who take a placebo have an effect, if only for
a short time. Participants will not know whether participants are receiving placebo
stimulation or electrical stimulation, but that information is available if it is needed. In
the remainder of the description of what will be done, both the electrical stimulation and
the placebos stimulation will be called "stimulation."

Stimulation will be completed with a Transcranial Direct Current Stimulator. This is an
experimental device that is not currently approved by the Food and Drug Administration (FDA)
for any treatment. Participants will receive stimulation for up to 20 minutes. To perform the
stimulation, Investigators will either apply two salt-water soaked sponges to their head or
five smaller gel covered disk electrodes. Gel-covered disk electrodes are placed in specially
designed holders held in a cap that fits on their head. Caps are fitted to their head size
for comfort. Following the stimulation, Investigators will remove the sponges or electrodes
and have participants perform a series of computerized tests to assess their cognitive
ability. These involve tasks where participants will have to respond to images or sounds
presented by a computer screen or headphones.

Participants may also be asked to undergo magnetic resonance imaging (MRI) of their brain
before, during, and after undergoing transcranial direct current stimulation. Investigators
will use an MRI safe Transcranial Direct Current Stimulator to perform stimulation and
evaluate how their brain responds to stimulation. Magnetic resonance imaging (MRI) is a
procedure that allows doctors to look inside the body by using a scanner that sends out a
strong magnetic field and radio waves. This procedure is used routinely for medical care and
is very safe for most people, but participants will be monitored during the entire MRI scan
in case any problems occur. The risks of MRI are:

The MRI scanner contains a very strong magnet. Therefore, participants may not be able to
have the MRI if participants have any type of metal implanted in their body, for example, any
pacing device (such as a heart pacer), any metal in their eyes, or certain types of heart
valves or brain aneurysm clips. Someone will ask participants questions about this before
participants have the MRI.

There is not much room inside the MRI scanner. Participants may be uncomfortable if
participants do not like to be in close spaces ("claustrophobia"). During the procedure,
participants will be able to talk with the MRI staff through a speaker system, and, in the
event of an emergency, participants can tell them to stop the scan.

The MRI scanner produces a loud hammering noise, which has produced hearing loss in a very
small number of patients. Participants will be given earplugs to reduce this risk.

Inclusion Criteria:

- Healthy adult

- Eligible to undergo an MRI

Exclusion Criteria:

- History of neurologic disease or dementia

- History of psychiatric disease which required hospitalization, or

- Current depression

- History of head trauma with unconsciousness

- Developmental learning disability (e.g., dyslexia, dyscalculia)

- History of vital organ failure (e.g., heart, lungs, kidneys, liver)

- Currently taking any psycho-active medications

- Pregnancy