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biological underpinnings of therapeutic effects. With ing from anxiety (16), depression (3,34), headaches,
proper evidence guiding the use of neuromodulation drug withdrawal symptoms (72), fibromyalgia (24),
therapies, these methods could be used to treat a post-traumatic stress disorder (PTSD) (35,57), and
number of complex disorders or serve as a valuable even bipolar depression (43). Most of these studies
addition to established treatment paradigms. demonstrate positive effects of CES on these disorders
As these technologies are being recognized and and include symptom reduction with minimal side
optimized, the research regarding the clinical poten- effects. There have even been a few studies that have
tial has evolved. Thus, the purpose of this manuscript demonstrated positive effects on learning paradigms
is to review the current magnetic resonance imag- that are interpreted as influencing neuroplasticity
ing (MRI) literature for more objective evidence (32). However, there is a need for additional research
of treatment efficacy or biological insights into the before the biological mechanisms of action are clearly
brain changes associated with three common neu- understood (58).
romodulation techniques (cranial electrotherapy MRI as a technological means of assessing struc-
stimulation (CES), transcranial direct current stimu- tural and functional change in the brain before, during,
lation (tDCS), and transcranial magnetic stimulation and after treatment presents a plausible method of
(TMS)). Though there are a number of different ways examining the effects of CES. Structural and func-
to measure or image the effects of these neuromod- tional differences in the brain are often observed in a
ulatory methods on the brain, the main focus of this number of the disorders for which CES is indicated
review is on the use of various MRI sequences. Each (33,45,50), and regularization/minimization of these
neuromodulation technique is described briefly below, differences could be used as a way of understanding
and the current imaging literature supporting/disre- the biological or neuroplastic changes that occur
garding these treatments is then summarized. in the context of treatment. Currently, there are no
structural MRI studies of therapeutic effects following
Cranial Electrotherapy Stimulation (CES) CES. Structural and more advanced MRI methods
In the United States, CES technology is classified such as diffusion weighted or diffusion tensor imag-
by the Food and Drug Administration (FDA) as a ing (DWI/DTI) might prove useful in demonstrating
Class III medical device and is approved for the treat- structural connectivity. The physics behind DWI/DTI
ment of insomnia, depression, anxiety, and pain. CES acquisition, the growing number of ways to examine
is a non-invasive device that uses transcutaneous these data, and the studies that demonstrate changes
pulsed microcurrents of less than 1000 µA to the in connectivity combined with the positive results
head, usually with electrodes applied to the ear lobes of CES seen in the controlled studies provide fertile
or scalp. Dosage can be managed by the individual, ground for investigating the effects of CES with MRI.
and a therapy session usually ranges from 20 to 60 Though there are currently no significant struc-
minutes. Reports of adverse effects (e.g., slight tin- tural MRI findings supporting CES, functional MRI
gling sensation at the electrode site, lightheadedness, methods have been used. One advanced MRI method
dizziness) from CES therapy are rare, with CES users that has been used is resting state functional MRI
generally reporting more positive experiences. (rsfMRI). rsfMRI allows researchers to characterize
CES is thought to generate its effects by direct the large-scale organization of the neural networks by
action on the brain, but the exact mechanism by looking at the temporal relationship of the changes
which the electrical current from CES alters brain (how one signal changes in time relative to another
function remains somewhat unclear. Early electro- signal in time) of the blood-oxygenated-level-de-
encephalographic (EEG) studies found changes dur- pendent (BOLD) signals from throughout the brain.
ing and after CES treatment, including alpha EEG Examination of these signals when the person is not
wave changes similar to trained meditators (18,73). actively engaged by a task in the scanner (at rest) has
There are also a number of controlled studies that documented the default mode network (DMN) (66),
show benefits of CES treatments for patients suffer- the functional connectivity pattern the brain reverts