Non-invasive brain stimulation for chronic aphasia has been reported as one of the effective therapeutic strategies. Previous studies on aphasia treatment have shown the evidences of enhancing language recovery by using rTMS and tDCS. Although optimal sites for stimulation to induce recovery can vary across protocols or patients, there have been two major approaches. One is the functional enhancement of the lesional/peri-lesional area, and the other is that of the left inferior frontal gyrus (IFG) including Broca area. For rTMS, to minimize the risk of epilepsy, low-frequency rTMS has been applied to suppress the healthy side (right) to increase the language function of the left hemisphere by reducing the transcallosal inhibitory projection (Naeser, 2005). In contrast, anodal tDCS to facilitate the affected side (left) or cathodal one to suppress the healthy side can be used. However, detailed comparison of these possible protocols in a homogenous cohort has never been done so far.
The purpose of this study is to compare various intervention strategies using non-invasive brain stimulation in a single case by measuring the short-term effects with cross-over design.
The case is a 48 year-old man who suffered from the left temporal subcortical hemorrhage (middle temporal gyrus: MT) due to brain arteriovenous malformation (AVM) at the age of 44. After AVM resection, he received rehabilitation of Speech for 5months. At the time of this study, he was 2-years post-stroke and had mild amnesic aphasia. We performed a single intervention of 1-Hz rTMS (20 min, 90% of rest motor threshold) at the right MT or IFG, and anodal/cathodal tDCS to the left/right MT or IFG (2mA, 20 min) in a cross-over design. Language performance was evaluated by the error-rate and reaction times (RT) of the picture-naming test.
We found the significant improvement in RT for the 1-Hz rTMS at the right IFG and the anodal tDCS to the left IFG but not for the other protocols.
In accord to previous studies, we showed the relevance of IFG for the target of brain stimulation for aphasia rehabilitation. Customization of brain stimulation strategy for each patient might be useful for effective neurorehabilitation.