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EVALUATION OF NEUROMODULATION USING MRI 41

to when at rest. Importantly, there are a number of contact between the apparatus and the subject (74).
studies that have shown that unique alterations in Of note, the properties of cerebrospinal fluid and
the DMN occur in patients with different disorders, surface properties of the brain likely produce a wider
including anxiety, depression, and acute/chronic pain area of effect than the target location for stimulation
(11,26,27). A preliminary study of healthy control (89).
participants indicated a significant change in the TMS can be delivered through different techniques
DMN and cortical deactivation, especially at the (single, paired, and repeated) to produce either a
higher frequency (100-Hz) CES stimulation (19). disruptive, excitatory, or inhibitory effect on cortical
These specific changes in the DMN and cortical acti- function (74,89). The excitatory, or facilitative, effect
vation patterns could lead to the therapeutic effects on motor cortex was the rationale for repetitive TMS
seen in clinical studies by altering thought patterns (rTMS) treatment of depression. The facilitative effect
(e.g., worry or rumination) and promoting attention of TMS has been demonstrated to persist for days
to other stimuli (e.g., surrounding environment). to weeks following a series of rTMS treatments (87).
However, these potential therapeutic effects remain The inhibitory effect of TMS delivered to a specific
speculative currently and require additional studies. location has been extensively utilized in cognitive
From this review of the literature, it is clear that neuroscience to understand structural-functional
CES has positive results in a number of different relationships in the brain (74). In part because of
clinical settings. The literature certainly could benefit the ability to produce facilitative or inhibitory effects,
from clinical trial methodologies (e.g., randomization,
placebo, cross-over designs, etc.) and more direct
observation of brain changes using advanced tech-
nologies like MRI. Future studies will be important in
not only helping to characterize the functional effects
of CES and elucidate the biological underpinnings
of CES efficacy, but may very well lead to improved
methods CES treatment (e.g., better delivery, dosage
requirements, improved target accuracy).

Transcranial Magnetic Stimulation (TMS)
TMS is a noninvasive method of targeting and
stimulating brain areas via the induction of a strong
electromagnetic field. This magnetic field is created
using a coil placed near the head that produces ion
movement within brain tissue orthogonal to the
magnetic coil. Spatial acuity and penetrability of the
magnetic pulse are determined by variations in coil
size and design. TMS is generally safe and well-tol-
erated, has received FDA approval for clinical use in
treatment-resistant depression (59), and is generally
associated with only a few mild adverse effects (e.g.,
minor pain, scalp discomfort) when appropriate
protocols are followed (40,88). It also represents
an improved method of cortical stimulation over
electric stimulation due to its improved ability to
permeate bone, comparatively reduced signal loss Figure 1. A typical TMS equipment configuration showing the
across distance, and the lack of a need for physical capacitor/switch and “figure 8” stimulator coil (end of blue cable).