Cathodal transcranial direct current stimulation of the right Wernicke’s area improves comprehension in subacute stroke patients
Introduction
Aphasia is a disturbance of language caused by brain injury to the left cerebral hemisphere (Jordan & Hillis, 2006). Stroke is the most common cause of aphasia, and about 20% of stroke patients develop aphasia (Naeser et al., 2005a).
Aphasia treatments include speech and language therapy and pharmacologic therapy (Greener et al., 2001, Walker-Batson et al., 2001), but several studies have found that these treatments are not effective for patients with aphasia (Greener et al., 2001, Lincoln et al., 1984). Therefore, there is a need for new treatments that show greater improvements in patients with aphasia.
Transcranial direct current stimulation (tDCS) and repetitive transcranial magnetic stimulation (rTMS) are new approaches for non-invasive brain stimulation that have been shown to modulate excitability in the brain (Fitzgerald et al., 2006, Paulus, 2003). Among the advantage of tDCS over rTMS are increased patient comfort, a broader area of stimulation, simultaneous speech training, and fewer side effects. Cathodal tDCS has been found to decrease cortical excitability, and anodal tDCS has been found to increase excitability and to potentiate N-methyl-D-aspartate action (Liebetanz et al., 2002, Vines et al., 2006). To date, tDCS has been utilized primarily to help stroke patients recover motor functioning, and tDCS has been found to improve motor skills (Hummel et al., 2005).
The left superior temporal cortex has been associated with language processing and improved comprehension in patients with aphasia (Price, 2000), but activation of the right hemisphere may facilitate transcallosal disinhibition, which is less conducive to language recovery in right-handed acute post-stroke aphasia patients (Winhuisen et al., 2005).
Although naming improved after tDCS in stroke patients with non-fluent aphasia (Monti et al., 2008), little is known about the effects of tDCS on the recovery of comprehension from global aphasia after stroke.
Thus, we assessed whether activating the left superior temporal gyrus or the suppressing the contralateral portion of Wernicke’s area via tDCS could ameliorate the symptoms of aphasia, including those related to comprehension capacity, in subacute stroke patients.
Section snippets
Subjects
This was a single-center, prospective, double-blind, sham-controlled study. We evaluated 78 patients with subacute middle cerebral artery (MCA) ischemic infarct who were hospitalized in the rehabilitation department of the Asan Medical Center, Seoul, Korea, between April 2007 and May 2009. Magnetic resonance imaging (MRI) was performed to confirm both the clinical diagnosis of ischemic stroke and the lesion location. Patients with other types of stroke (e.g., hemorrhagic) were not included to
Results
We evaluated 78 MCA ischemic infarct patients, 33 of whom met our inclusion criteria. These 33 patients had left M1 or M2 MCA infarct and were not taking pharmacological drugs, which may affect brain modulation. All patients were randomized into cathodal (n = 11), anodal (n = 10), and sham (n = 12) tDCS groups. Within the groups, four, three, and five subjects, respectively, dropped out of our study before it was completed. Seven patients were discharged early, three patients refused tDCS therapy due
Discussion
This study was designed to examine the effects of tDCS on patients with global aphasia following a subacute stroke. During the comprehension of speech, Wernicke’s area receives polymodal information and processes these data to select an appropriate word (Seltzer & Pandya, 1994). Thus, dysfunctions in Wernicke’s area have been associated with comprehension disabilities. To improve comprehension ability, we therefore stimulated the superior temporal gyrus CP5 in the left hemisphere or CP6 in the
Conclusion
This is the first study to show that application of contralesional cathodal tDCS during speech therapy in subacute global aphasia stroke patients with left MCA ischemic infarct results in improvements in comprehension. Cathodal tDCS over the right Wernicke’s area, combined with speech therapy, was more effective than speech therapy alone, suggesting that inactivation of contralesional neural overactivity is therapeutic. Our findings suggest that tDCS may provide an adjuvant treatment approach
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