In Vivo Imaging of Therapeutic Electric Current Flow

Transcranial direct current stimulation (tDCS) and deep brain stimulation (DBS) are examples
of electrical stimulation therapies that are rapidly gaining attention as means of modulating
motor function, semantic processing, and executive function. Both therapies have attracted
many clinical and experimental studies. tDCS has been found to have both facilitatory and
inhibitory effects on the brain depending on stimulation polarity and electrode position. DBS
has been thoroughly evaluated clinically for treatment of movement disorders, principally
Parkinson's disease, and is extending its reach to include treatment of disorders such as
focal dystonia, depression and chronic pain. While still mostly in the experimental stage,
tDCS applications and acceptance are growing extremely rapidly.

Although the functional alterations associated with tDCS can be categorized without knowledge
of the underlying neurophysiology, an understanding of where externally applied current
actually flows in any electrical stimulation technique is crucial as a basis for
understanding which brain regions, circuits, or elements are affected by these therapies, and
how these changes may occur. Such knowledge will lead to a better understanding of the
mechanisms underlying these therapies, and thus to more focused and effective stimulation
patterns and locations. Ultimately, this will lead to more efficient and novel clinical
applications.

Many studies have simulated the effects of current application in both extra- and
intracranial modalities using computer simulation. Simulations will always be limited by
errors in interpreting MRI data during segmentation, differences between assumed and actual
electrical conductivity values, and mismatches between actual and presumed electrode
locations and sizes. Thus, better methods to understand and verify current flow distributions
are badly needed.

In this study a recently developed MRI-based phase imaging technique to more directly measure
current densities in vivo. Unlike earlier MRI-based methods of measuring electrical current
flow, the technique works without requiring subject repositioning. This methods will be
validated against high-resolution subject-specific models incorporating many tissue
compartments, including anisotropic white matter. Thus, a new direct measurement method
against state-of-the-art modeling approaches.

Inclusion Criteria:

- right handed (as determined by the Edinburgh battery),

- English as native language.

Exclusion Criteria:

- appreciable deficits in hearing,

- appreciable problems with articulation,

- appreciable accent schizophrenia, bipolar disorder, or major depression,

- 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 active or prior history of seizure disorder, family history of seizure disorder,
prescribed seizure inducing medication.