Transcranial Magnetic Stimulation (TMS): Potential Progress as an Alternative Treatment for Language Improvement in Aphasia, Reports psychiatrist, Dr. Gregory Marsella from his South Florida Chrysalis TMS Institute
Elizabeth E. Galletta, PhD, Paul R. Rao, PhD, and Anna M. Barrett, MD
Aphasia researchers and clinicians share some basic beliefs about language recovery post stroke. Most agree there is a spontaneous recovery period and language recovery may be enhanced by participation in a behavioral treatment program. The application of biological interventions in the form of pharmaceutical treatments or brain stimulation is less well understood in the community of people who work with individuals having aphasia. The purpose of this article is to review the literature on electrical brain stimulation (TMS) as an intervention to improve aphasia recovery. The article will emphasize emerging research on the use of transcranial magnetic stimulation (TMS) to accelerate stroke recovery. We will proﬁle the current US Food and drug Administration (FDA)–approved application to depression to introduce its potential for future application to other syndromes such as aphasia
TMS had its origins in the mid 1980s as an exercise in scientific curiosity. A medical scientist in England had discovered that a strong magnetic pulse directed into a brain (his own) evoked a striking effect on his body - it made his thumb 'twitch' involuntarily. This vivid demonstration of the interaction of magnetism and brain tissue quickly got the attention of psychiatrists: they foresaw in the technique, a benign way to stimulate parts of the brain involved in mental illnesses such as depression to improve patients' health.
Research-clinical interventions for stroke survivors with aphasia intend to activate dysfunctional brain networks supporting linguistic processing and communicative intent. These interventions may generally fall into 3 broad categories: speech-language rehabilitation treatment; pharmaceutical treatment; and direct brain-stimulation therapies, such as transcranial magnetic stimulation (TMS). Aphasia researchers and clinicians agree that there is a spontaneous language recovery period post stroke and that language recovery may be enhanced by participation in a behavioral rehabilitation treatment program.
How biological interventions such as pharmaceutical treatments or brain stimulation can enhance function in the recovering brain is generally less well understood among clinicians working therapeutically with individuals having aphasia. Biological interventions in the form of pharmaceuticals are currently administered to stroke survivors with aphasia to treat co-morbid diagnoses, such as anxiety or depression, rather than directly administered for the clinical application to treat language recovery. Many practitioners accept that medication treatment (antidepressants) for depression post stroke may have a secondary positive effect on post stroke recovery.
Moreover, experimental research for the use of pharmaceuticals for direct language recovery has also suggested that pharmaceutical treatment can improve communication.
These approaches are not yet used in the clinical treatment of aphasia perhaps due to obstacles to the knowledge transfer to clinical care secondary to basic science researchers having little interface with clinicians. This is less of an issue with another relatively recent research treatment for language recovery, TMS, a new biological treatment with current promise in language-rehabilitation research. The purpose of this article is to review the literature on brain-stimulation therapies for aphasia. Speciﬁcally, TMS will be described, with its current US Food and drug Administration (FDA)–approved application to depression
Background on TMS
TMS is a tool used to electrically stimulate brain tissue. It is a noninvasive procedure that creates electrical currents in speciﬁc brain regions. An insulated copper coil in the shape of a ﬁgure eight is placed over the scalp. A strong, brief electrical current ﬂows through the coil, and the current induces a rapid transient magnetic ﬁeld in the brain tissue directly below the placement of the coil. The induced magnetic ﬁeld secondarily induces electric current ﬂow in the cortex in the region parallel to the coil, at a depth of approximately 1 cm, which causes a depolarization or spiking of neurons in the brain. The participant hears a brief clicking noise and may feel a slight scalp sensation. Typically, participants report the procedure is painless. However, stimulation can be painful, and headaches, and very rarely seizures, have been reported post TMS. TMS is a focal, nonsystemic approach with much potential for the treatment of neuropsychological conditions. A TMS-induced change in neural ﬁ ring may lead to behavior changes; this allows researchers to infer that brain areas that are stimulated may play a necessary role in supporting the studied cognitive functions. This procedure has been used for diagnostic and therapeutic purposes, with an approved therapeutic application for a subset of people with depression.
There are 3 basic types of TMS: single-pulse, paired pulse, or repetitive TMS (rTMS). In singlepulse TMS, one pulse is applied no faster than once every few seconds. In paired pulse, there are 2 pulses applied out of phase to inhibit or excite neurons within the same hemisphere or to inhibit neurons in one hemisphere while exciting them in the other hemisphere. In rTMS, magnetic pulses are delivered in a rapid series or "train." When rTMS is used, multiple single-pulse stimuli are presented at a speciﬁc frequency, intensity, and time duration. This facilitates an excitation or inhibition of activity in the affected cortical area. An example of slow rTMS at 1 Hz (inhibitory) means that one magnetic pulse is applied every second (one cycle per second). An example of fast rTMS at 10 Hz (excitatory) means that 10 magnetic pulses are administered every second (10 cycles per second).
The intensity of the signal administered is participant speciﬁ c and is based on a percentage of each individual's resting motor threshold (RMT) at any given point in time. The resting motor threshold (RMT) is deﬁned as the minimal stimulation intensity needed to produce motorevoked potentials (activating muscle ﬁbers in a target muscle such as in the hand). Use of TMS to activate muscles and determine the threshold for activation takes place before TMS is applied to brain areas to study cognitive function such as language (since motor cortex may not critically support language-related cognition). Intensity is determined for each individual just prior to each TMS application. Duration of the TMS pulse is usually ﬁxed within experiments and is not participant dependent.
Application of TMS to Aphasia
As trials look at the application of TMS for subgroups of depressed populations (eg, depression in pregnancy, postpartum, and in Parkinson's disease), perhaps these explorations can support initial evaluations regarding the application of TMS to aphasia. The TMS application for depression may serve as a model for TMS utilization for the improvement of speech and language. There is currently no FDA approval for the application of TMS to people with post stroke aphasia or for any neurologic or neuropsychological condition other than severe depression.
Much of the research in the area of impaired language has used rTMS to modulate interhemispheric interaction so as to support language recovery. It is used to inhibit what is thought to be overactivation of the right hemisphere homologue after a left hemisphere stroke. Although it may seem surprising that the use of rTMS to inhibit the right hemisphere could actually improve language, there have been animal studies and some case reports in humans that suggest that neural damage to speciﬁ c areas in the brain (in the case of aphasia, contrateral to the lesion) may promote improved behavior or function of certain conditions. Support for this use of rTMS to inhibit overactivation of the unimpaired hemisphere is also derived from studies that have demonstrated increased right hemisphere blood ﬂow after left hemisphere stroke utilizing functional magnetic resonance imaging (fMRI), suggesting that the right hemisphere may change (ie, become overactivated) by the brain damage that occurred in the left hemisphere. Moreover, case studies that documented improved behavioral function after a lesion in the presumed contralateral hemisphere also supported a theory that overactivation of the right hemisphere may interfere with language recovery post stroke. For example, Helm-Estabrooks reported improved speech ﬂuency in an individual with a history of chronic perseverative stuttering after a head injury, suggesting that the acquired brain injury had a positive effect on speech. In summary, documented overactivation in the right hemisphere post stroke and case reports noting changes in function after brain damage led to the idea that a reduction in right brain activation may improve stroke recovery (paradoxical functional facilitation). However, other researchers suggested that right brain activation may improve recovery when interhemispheric interaction is optimized.
Devlin and Watkins review the existing literature on TMS use for language. Research that investigated the impact of TMS on normal speech production and for the recovery of speech and language post stroke is described. Both studies that implement single-pulse TMS and rTMS are reported, with the rTMS used to inhibit pathologic overactivation of the right hemisphere Broca's area homologue region. According to Naeser et al, improved picture naming after rTMS for 4 patients even 2 months after the treatment had stopped is encouraging. Moreover, a recent case report by Hamilton and colleagues indicated that use of rTMS had a positive effect on discourse (a picture description task) as well as naming, which suggests that the use of rTMS in conjunction with behavioral treatment may promote a positive prognosis for language recovery post stroke for some people.
Future Research on TMS Use and Aphasia
Current research on TMS use with aphasia is still at the small-scale study or "proof of principle" stage. Only relatively few research groups are investigating its application by intensive examination of a relatively small set of individuals with no control groups (eg, Naeser et al).
In this review, we introduced noninvasive brain stimulation as a method being developed to research and support poststroke recovery of aphasia. Although we have described the initial steps that have been taken to promote the future clinical use of TMS for aphasia, there is still much work to be done. If this method moves forward toward clinical application, we hope future studies will uncover feasibility obstacles, subject characteristics important to treatment response, and ideal combinations of behavioral and noninvasive stimulation.