68 CHAPTER 2
INVASIVE TECHNIQUES: STIMULATING FROM THE INSIDE A specific type of ESB called deep
brain stimulation (DBS) has been shown to be very helpful in some disorders in humans. In
this procedure, neurosurgeons place electrodes in specific deep-brain areas and then route
the electrode wires to a pacemaker-like device called an impulse generator that is surgi-
cally implanted under the collarbone. The impulse generator then sends impulses to the
implanted electrodes, stimulating the specific brain areas of interest. DBS has been widely
used as a treatment for Parkinson’s disease and may play an important role in the treat-
ment of seizure disorder, chronic pain, and possibly some psychiatric disorders (Fisher
et al., 2010; Rabins et al., 2009; Weaver et al., 2009), among other areas. Also, using DBS
for specific disorders allows researchers to learn about other effects DBS may have on the
brain such as affecting an individual’s mood or memory. It should be noted that invasive
techniques such as DBS are typically only used after all other less intrusive treatments have
been shown to be ineffective or whose side effects have been deemed undesirable. For
example, DBS is being investigated for the treatment of anorexia nervosa in individuals for
whom other treatments have not been effective (Lipsman et al., 2013).
One of the newest and fastest developing areas in brain stimulation is optogenetics,
where neurons can be activated by light rather than electricity. While currently only used in
animal models, it is being employed across a variety of areas to enhance our understanding
of the brain, cognition, and behavior (Burguière et al., 2013; Miocinovic et al., 2013). Further-
more, the technique is not only being used to refine existing DBS methods, it is also being
paired with other methods, such as fMRI, to further enhance our understanding of brain
function in both normal and disordered behavior (Creed et al., 2015; Ferenczi et al., 2016).
NONINVASIVE TECHNIQUES: STIMULATING FROM THE OUTSIDE There are also noninvasive
techniques for stimulating the brain that contribute to research and our knowledge of
the brain in a variety of areas. In transcranial magnetic stimulation (TMS), magnetic pulses
are applied to the cortex using special copper wire coils that are positioned over the
head. The resulting magnetic fields stimulate neurons in the targeted area of the cortex.
Longer-lasting stimulation results when the pulses are administered in a repetitive fash-
ion, which is referred to as repetitive TMS (rTMS). Another procedure, called transcranial
direct current stimulation (tDCS), uses scalp electrodes to pass very low-amplitude direct
current to the brain to change the excitability of cortical neurons directly below the elec-
trodes. Both rTMS and tDCS are being evaluated as research tools in studies of cognition
such as memory retrieval and decision making (Boggio et al., 2010; Boggio et al., 2009)
and as possible treatment options for a variety of psychological disorders including post-
traumatic stress disorder (PTSD) and depression and physical disorders due to suffering
a stroke (Boggio, Rocha, et al., 2009; Nitsche et al., 2009; Williams et al., 2010).
Bear in mind that stimulating the cortex may facilitate specific functions or behav-
iors but impair others. For example, if someone is counting from 1 to 20 and the brain is
stimulated in the correct location of the motor cortex, the person’s speech would be dis-
rupted, but perhaps stimulating in other areas of the frontal lobe may assist the person
in attending to the counting task. Furthermore, the brain has widespread connections, so
stimulation in one area is likely to affect other areas. In one study, inhibitory stimulation
of the left prefrontal cortex resulted in reduced blood oxygenation on both the left and
right sides of the prefrontal cortex (Tupak et al., 2013).
Note: tDCS is NOT the same as electroconvulsive therapy, which uses much higher
levels of current through the entire brain, resulting in a grand mal seizure and changes
in the brain chemistry associated with depression. to Learning Objective 15.11.Neuroimaging Techniques
2.9 Compare and contrast neuroimaging techniques for mapping the structure
and function of the brain.
All of these methods of stimulation yield important information about the brain and
behavior, but they do not allow us to see what is going on with the brain as a whole.This person is participating in a study that
involves repetitive transcranial magnetic
stimulation (rTMS). This procedure uses
magnetic pulses to stimulate specific areas
of the cortex. rTMS is being used in both
studies of cognition, as seen here, and in
the exploration of new potential treatments
for a variety of psychological disorders.