The right hemisphere is not unitary in its role in aphasia recovery

Abstract

Neurologists and aphasiologists have debated for over a century whether right hemisphere recruitment facilitates or impedes recovery from aphasia. Here we present a well-characterized patient with sequential left and right hemisphere strokes whose case substantially informs this debate. A 72-year-old woman with chronic nonfluent aphasia was enrolled in a trial of transcranial magnetic stimulation (TMS). She underwent 10 daily sessions of inhibitory TMS to the right pars triangularis. Brain activity was measured during picture naming using functional magnetic resonance imaging (fMRI) prior to TMS exposure and before and after TMS on the first day of treatment. Language and cognition were tested behaviorally three times prior to treatment, and at 2 and 6 months afterward. Inhibitory TMS to the right pars triangularis induced immediate improvement in naming, which was sustained 2 months later. fMRI confirmed a local reduction in activity at the TMS target, without expected increased activity in corresponding left hemisphere areas. Three months after TMS, the patient suffered a right hemisphere ischemic stroke, resulting in worsening of aphasia without other clinical deficits. Behavioral testing 3 months later confirmed that language function was impacted more than other cognitive domains. The paradoxical effects of inhibitory TMS and the stroke to the right hemisphere demonstrate that even within a single patient, involvement of some right hemisphere areas may support recovery, while others interfere. The behavioral evidence confirms that compensatory reorganization occurred within the right hemisphere after the original stroke. No support is found for interhemispheric inhibition, the theoretical framework on which most therapeutic brain stimulation protocols for aphasia are based.

Copyright © 2011 Elsevier Srl. All rights reserved.

Figures

Fig. 1. Locations of Strokes

(A) T1 weighted MRI showing LH stroke causing initial aphasia (acquired 4 years after the stroke). (B) Diffusion weighted image showing the acute RH stroke. The white arrow shows the right pars triangularis therapeutic TMS target.

Fig. 2. fMRI and Acute TMS Results

(A) Change in naming performance induced by inhibitory TMS to each of the candidate therapeutic TMS targets. (B) Baseline fMRI data (naming > pattern viewing) shown with locations of candidate TMS targets. (C) Change in fMRI activity after inhibitory TMS to the inferior posterior pars triangularis (yellow) target. The significance threshold is p

Fig. 3. Behavioral Effects of TMS and RH Stroke

Raw scores were Z-transformed based on mean and SD of baseline measurements to allow comparison across measures. The gray area indicates the significance threshold for a p st 30 = accuracy on the first 30 items of the Boston Naming Test. Repetition and Comprehension measures are subtests of the BDAE