Lesion correlates of transcranial direct current stimulation (tDCS) in chronic nonfluent aphasia
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1
UNIVERSITY OF PENNSYLVANIA, Laboratory for Cognition and Neural Stimulation, United States
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2
University of Pennsylvania, Perelman School of Medicine, United States
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3
University of Pennsylvania, Department of Neurology, United States
A growing body of evidence suggests that tDCS may facilitate language recovery in patients with chronic aphasia [1]. Until recently, it was not clear whether individual patients would respond differently to different patterns of stimulation. We addressed this concern in our recent work by examining how patients with chronic nonfluent aphasia would respond to different placements of electrodes (or montages), targeting the left and right frontal areas [2]. However, the anatomic correlates of responsiveness to tDCS with a particular montage are unclear. We sought to explore this question in the current study with the hypothesis that patterns of brain damage within the frontotemporal language network would predict response to different tDCS electrode montages.
Twelve patients underwent stimulation with 4 active montages (anode/cathode over left/right frontal sites) and 1 sham condition. For active montages, 2 mA current was delivered through 5cm x 5cm electrodes for 20 minutes. An optimal montage was determined in each patient by measuring the picture naming ability before and after stimulation. A single neurologist delineated lesions in MRIcron, using clinical images obtained during or after each patient’s medical treatment for stroke. Lesion overlap and subtraction plots were generated to compare the location and extent of brain damage in relation to the optimal montage.
In 8 out of 12 patients, significant improvement in picture naming ability was found following stimulation with at least one montage. The optimal montage varied across patients: 3 patients responded to the left-anode, 3 to the left-cathode and 2 to the right-cathode montages (responders), and 4 patients did not respond to any montage (nonresponders). None responded to sham or the right-anode montage [2]. Assessment of maximal lesion overlaps in the responder-subgroups—left-anode, left-cathode and right-cathode—suggested that different patterns of damage within the frontotemporal language network were involved. Superior and middle temporal areas were more frequently damaged in the patients who responded to the right- and left-cathode montages compared to those who responded to the left-anode. Among those who responded to cathodal stimulation, the inferior and middle frontal, the middle temporal areas, and the surrounding white matter pathways were more frequently damaged in those who responded to the left-cathode compared to the right-cathode montage.
We conclude that patients exhibiting differential patterns of damage involving the frontotemporal language areas may respond to stimulation differently. Integrity of left temporal language areas appears crucial for responsiveness to the anodal or excitatory stimulation of the damaged, left frontal areas. If temporal areas are not spared, extensive damage in specific frontotemporal areas including the surrounding white matter predicts responsiveness to cathodal or inhibitory stimulation of the left frontal areas. We posit that tDCS-induced normalization of the intra-hemispheric inhibition [3] may be the underlying mechanism of improvement in these patients.
References
1. Shah, P.P., et al., Induction of neuroplasticity and recovery in post-stroke aphasia by non-invasive brain stimulation. Frontiers in Human Neuroscience, 2013. 7.
2. Shah, P., et al., Individualized treatment with transcranial direct current stimulation in patients with chronic nonfluent aphasia due to stroke. Neurology, 2014. 82(10): p. Supplement S21.007.
3. Monti, A., et al., Improved naming after transcranial direct current stimulation in aphasia. Journal of Neurology Neurosurgery and Psychiatry, 2008. 79(4): p. 451-453.
Keywords:
Nonfluent aphasia,
tDCS,
Stroke,
Neurorehabilitatation,
Speech Therapy,
lesions
Conference:
Academy of Aphasia -- 52nd Annual Meeting, Miami, FL, United States, 5 Oct - 7 Oct, 2014.
Presentation Type:
Platform or poster presentation
Topic:
Not student
Citation:
SHAH
PP,
Norise
C,
Garcia
G,
Torres
J,
Faseyitan
O and
Hamilton
RH
(2014). Lesion correlates of transcranial direct current stimulation (tDCS) in chronic nonfluent aphasia.
Front. Psychol.
Conference Abstract:
Academy of Aphasia -- 52nd Annual Meeting.
doi: 10.3389/conf.fpsyg.2014.64.00017
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Received:
17 Apr 2014;
Published Online:
04 Aug 2014.
*
Correspondence:
Dr. Roy H Hamilton, UNIVERSITY OF PENNSYLVANIA, Laboratory for Cognition and Neural Stimulation, PHILADELPHIA, PA, 19104, United States, roy.hamilton@uphs.upenn.edu