Aphasia is a neurological communication disorder most often caused by stroke that damages the left hemisphere of the brain where language processing occurs. Two promising neurorehabilitation treatment methods for aphasia are transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS), which use currents to stimulate brain areas and promote plasticity. Research shows these methods improve language skills like word recognition more than speech therapy alone. tDCS has advantages of lower cost and potential for self-administration but more research is still needed on both methods.

1. Aphasia: The Communication Disorder and
Analysis of Neurorehabilitaion Treatment Methods: transcranial direct current stimulation
(tDCS) and transcranial magnetic stimulation (TMS)
Catherine M. Christianson
Worcester State University

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Abstract
Aphasia is a broad term used to describe a neurological communication disorder that is most
often caused by stoke or injury to the brain. A diagnosis of aphasia is typically determined by
finding damage to the left hemisphere of the brain, where our primary language processing
centers are housed. Characteristics of those with aphasia vary depending on the site of brain
lesion and severity of trauma to the brain. Typically, lesion sites that fall inside the Perislyvian
language zone exhibit the more significant deficits in language skills. There is much evidence
supporting specific site of lesion in the brain with an associated aphasia description, though more
research needs to be conducted on this topic. There is a growing amount of important placed on
improved treatment methods other than speech therapy. Various names of similar treatment fall
under the term neurorehabilitaion. Specific types of neurorehabilitaton include tDCS
(transcranial direct current stimulation) and TMS (transcranial magnetic stimulation). For
convenience, I will use the abbreviations tDCS and TMS as appropriate. Both methods include
sending currents directly into parts of the brain for stimulating effects. It is believed that this
manual brain stimulation helps the brain’s plasticity mechanisms better restore lost language
skills during the brain trauma or stoke event. Research reveals that the use of such methods
results in high correlation with recovering language processing skills such as word recognition
tasks or naming performance tests.

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Most cases of aphasia are the result of a stroke event, though other reasons for an
acquired aphasia include having a traumatic brain injury, a disease to the left hemisphere of the
brain, or a degenerative disease. (Coslett, B. 2011). In the United States, there is an incidence
rate of about 38% of people who are diagnosed with aphasia after coming out of a stroke (Rohde,
Worral, and Le Dorze, 994). Expressive and receptive types of aphasias have widely different
characteristics in terms of where content, form, or use deficits lay. For post-stroke aphasia
victims, it is not uncommon to see deficits in either language production, language
comprehension, or a combination of both (Torres, J., 2013). As stated by their names, Broca’s
Aphasia, and Wernicke’s Aphasia are named after their respective areas in the brain. Individuals
with Broca’s aphasia have issues with expressive language skills, such as producing non-fluent
speech. In an expressive language disorder, the individual with have difficulty with word
retrieval and thus word naming. Some with an expressive language issue might have acquired
this deficit due to a pyramidal system infraction and would have issues sending neurons to the
appropriate articulatory mechanism. Conversely, a receptive language issue such as in
Wernicke’s aphasia will encompass primary issues comprehending speech patterns. A
comprehension issue could reflect as a phonological disorder, where one will have extreme
difficultly discriminating the difference in speech sounds.
Both expressive and receptive language skills are needed for both efficient and effective
communication, hence there is a heightened importance on regaining these skills post-stroke in
those who have lost them. These are just two examples of an expressive and a receptive type of
aphasia disorder. Again, it is not uncommon to see both types of deficits on a varying scale for a
single patient. Current rehabilitation techniques for individuals with acquired aphasia are being
questioned for effectiveness in light of recent evidence suggesting alternative methods.
Though many who are the victims of a stroke and acquire aphasia do recover some
language skills soon after the incident, post-stroke recovery and rehabilitation outlook has been
shown to depend how plastic the patient’s brain is, or in other words how susceptible the
patient’s brain is to learning new language processes. Two compensatory features of the brain
have been observed to help with regaining language skills. New connections for language skills
have been observed to form in the surrounding the site of lesion. The other place of observed
connections is recorded in homotopic regions of the brain, usually the right hemisphere, though
this research is somewhat controversial in nature. (Torres, 2013). By targeting both these key

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areas of the brain with stimulation by magnetic currents, research has found significant positive
findings in patients attempting new language development compared to other treatments
administered. Current rehabilitation therapy may include speech therapy or a combination of
therapy in addition to use of pharmacological treatments, however those that are studying direct
brain stimulation methods want to know whether this would be an even more effective option for
a patient’s treatment (Chrysikou, Evangelia G., and Hamilton, Roy H., 2011). The most
commonly used treatment for aphasia victims is just speech therapy alone (Torres, 2013).
There are two highly-researched methods of direct brain stimulation that has prompted
further ongoing research. One such method is tDCS (transcranial direct current stimulation), and
the other, less-researched method is known as TMS (transcranial magnetic stimulation).
Implementation of one or the other method is determined on an individual case basis. Optimistic
findings, within the body of research that has been conducted over the past twenty years, reveal
significant improvements in language processing skills, such as word naming after
administration of both of these brain stimulating processes. These findings have been found in
individuals with post-stroke aphasia and even show significant improvements in other domains
apart from language, such as visuospatial processing and motor control when using tDCS and
TMS methods, when respectively appropriate (Torres, 2013). tDCS application has also been
shown to improve decision making skills and social interaction, implicating the therapeutic
strategy’s potential for use for not only those with an acquired aphasia but for those with
alternative deficits (Coslett, 2011). Both methods of direct brain stimulation work differently but
towards an identical goal: to help the brain in creating new language-specific networks. Further
research examining neural mechanisms during recovery are essential for determining which type
is more appropriate for the patient. Furthermore, there are distinct differences between the two
techniques that will also aid in determining appropriate therapeutic application. Some differences
include physiologic effects as well as practical differences of application (Torres, 2013).
TMS, or transcranial magnetic stimulation, is a therapeutic technique that involves
pulsing a relatively strong electric current, using copper wires attached to the skull, to painlessly
administer either a high or low frequency pattern. The systematic pulsing of the current will
result in stimulating either cortical inhibition or cortical excitation depending on what frequency
the TMS pulse is administered at. This stimulation has been the suspected catalyst for the brain’s
ability to form new language connections. The pulses can also be administered in different pulse

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patterns. These include single pulses, “timed paired” pulses, or in “trains of repetitive TMS,”
also referred to as rTMS pulses (Torres, 2013). The latter has been the most popular mode of
application. rTMS is an application that employs pulses at a predetermined rate of frequency,
with calculated expectations for lasting effects, post-application. This method can be used at
either a high or a low frequency in order to either decrease or increase cortical excitability
(Coslett, 2011).
One reason TMS is believed to be an effective therapeutic strategy is that it has been
shown to improve performance in a variety of language production tasks when combined with
speech therapy techniques. Some of these language production tasks include picture naming
(Torres, 2013). The TMS technique also helps researchers better locate specific cortical regions
and their corresponding linguistic functions. TMS as a therapeutic strategy has been researched
for effectiveness in patients who have healthy functioning. (Coslett, 2011).
Utilization of tDCS is a therapeutic strategy that also encompasses the administration of
currents onto the skull. tDCS, however, uses small currents through two surface electrodes that
have been soaked in a saline solution, and the two surface electrodes are then place strategically,
one in the surface of interest, probably on or around the brain’s site of lesion, and secondly onto
another distant area of the brain, for example, the opposing and supraorbital region of the brain
(Torres, 2013). It has been noted that tDCS is usually not strong enough to directly influence
cortical inhibition or excitation but can indirectly influence such cortical activity. tDCS is
primarily believed to modulate or directionally influence the brain’s action potentials (Torres,
2013). The longevity of the effects of tDCS vary depending on factors such as stimulation
duration, intensity, polarity levels, and locale of electrode placement on the skull (Coslett, 2011).
One reason tDCS is believed to be an effective therapeutic strategy is that the patient’s
assessment results not only boast elevated scores, post-treatment, but also a speedier recovery
time, again when used in conjunction with speech therapy (versus scores resulting from speech
therapy alone). Elevated testing results refer to slightly improved areas of visual processes,
motor learning (including coordination tasks), as well as decision-making, and social interaction,
working memory, tactile special acuity, and has even shown findings on temporary
improvements of overall cognitive functioning in Alzheimer’s and Parkinson’s disease, and
major depressions. Because of the optimistic findings after utilizing tDCS as a therapeutic
treatment option for those with other cognitive problem areas, there is a heightened interest on

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utilization for treatment on post-stroke victims with aphasic language deficits. (Polanowska,
K.E., 2013).
Another positive for using tDCS as a treatment option is that administration may
potentially be self-administered. This is highly motivating because speech therapy is known to be
costly for those with aphasia seeking treatment, and has been known to be difficult when looking
for proper personnel or resources. Speech therapy also imposes a significant time commitment
for the patient and his or her family. Also, research suggests that only intensive speech therapy
(over 98 total hours of therapy or more) has been shown notable positive outcomes. In other
words, for those who are administered with less than 98 hours, their tested level of learning was
not as competitive (Holland, R., 2012). It is suggested that speech therapy results in aphasia
rehabilitation are simply not consistent (Torres, J., 2013). For these reasons, alternate treatments
for aphasia patients have been considered other than just post-stroke surgery and speech therapy
administration.
It is important to consider the advantages and disadvantages of each method of treatment.
In addition to the basic differences of each approach, practical considerations including temporal
resolution, spatial resolution, differences in electrode placement, and physical portability must be
taken when assessing each case. Temporal resolution refers to the fact that with TMS, the effects
of TMS current stimulation are instantaneous, while in using tDCS, the effects are not as clearly
indicated. The result is a “low” temporal resolution for the doctor to interpret. It is obviously
better to have a clearer resolution, but other considerations may wave this factor in the decision-
making process between the two options. For example, in terms of spatial resolution, TMS has to
ability to affect large areas of the brain if need be, however this is not necessarily better; this
factor may be advantageous for some cases but not others. The differences in electrode
placement has been researched and have reflected differences in the strength of current
stimulation in focal points of the brain. The TMS method has been found as “more focal” and
predictable, however, it also shows variability in its effects, depending on the individual’s
personal amount of scalp and brain tissue between the electrodes. With tDCS, also shows
variance in effectiveness depending on hair and skull thickness in terms of administration. The
final consideration of portability may be a dealmaker or breaker. tDCS only requires “electrodes
and a small current stimulator that would fit in a briefcase,” while TMS requires a bulkier
generator, coils, and an MRI-guided system, and infrared camera, and “localizing tools” for

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neuronavigation purposes. If one can obtain the tools needed for TMS, all the better, however
that may certainly effect who is able to access each respective treatment method. (Torres, J.,
2013)
Further research is needed to evaluate neurorehabilitation’s role in aphasia rehabilitation
in terms of effectiveness (Holland, R., and Crinion, J. 2012). Further research on tDCS as a
therapeutic tool is also of high interest due to some of the factors listed above: more cost-
friendly, great ease of use, ease of administration, less time consuming, its versatility in use for a
wide variety of patients, noted minimal side effects, and, of course, its researched effectiveness
(Coslett, 2011). Other benefits include noninvasiveness and promise in treating somewhat
specific areas of language deficit. Disadvantages include access to tools needed and the fact that
more research needs to be conducted in terms of short-term and long-term efficacy as well as
safety concerns for use of brain stimulation over time. Promising research endeavors should
examine specific “structure-function” relationships between the location in the brain and its
respective language area. We want to be able to target specific language deficits with this type of
therapy in the future. Overall, I believe that both tDCS and TMS techniques show a great deal of
potential in terms of their effectiveness in aiding recovery of language skills for patients with
aphasia.

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References
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