Vasileios-Arsenios Lioutas, MD
Thiel A, Hartmann A, Rubi-Fessen I, Anglade C, Kracht L,Weiduschat, N.Effects of non-invasive brainstimulation on language networks and recovery in earlypoststroke aphasia. Stroke. 2013
Interventions targeting recovery from poststroke aphasia are important for the affected patients. Several non-invasive methods have been tested, including transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS). The underlying idea is that stimulation of specific cortical areas can modulate neurologic networks involved in human language. More specifically, there is a “shift” of function from the dominant to the non-dominant hemisphere following ischemic damage, a rearrangement that is thought to be detrimental to the language function. It follows that one of the main targets is limitation of this non-efficient shift, either by inhibiting the non-dominant hemisphere or by stimulating the dominant hemisphere.
In this interesting study, Drs. Tiel, Heiss et al, investigate the applicability of non-invasive brain stimulation in addition to standard speech and language therapy in the early phase of rehabilitation of patients with post-stroke aphasia. They applied inhibitory TMS in the right (non-dominant) posterior inferior frontal gyrus, using clinical as well as functional imaging (PET scan) markers before and after treatment. In addition to proving applicability of the method in a clinical setting the investigators found significant clinical improvement in the group that received TMS. More interestingly, the functional imaging correlate was found to be a “consolidation” of function in the dominant hemisphere; in other words the patients who received treatment, the shift of language function to the non-dominant side was significantly limited, lending support to the basic underlying principle.
The results are definitely very interesting and encouraging. But some points need to be taken into account: The patient sample was small (30 patients only), limiting the power of the study. For the same reason, subgroup analysis according to aphasia type was not possible; an issue that merits special attention. Additionally, questions regarding the most appropriate timing and duration of treatment are still under investigation. Although the concept of preventing rearrangement of language networks towards the non-dominant hemisphere seems to provide clinically meaningful results, it should be kept in mind that there is evidence for alternative methods, namely Melodic Intonation Therapy, whose success is based in the exact opposite principle: The right hemisphere is recruited, assuming language processing responsibilities that are normally left hemisphere function.
In summary, the current study is intriguing as a concept and yielded interesting results. However, the neuroplasticity of language neural networks is a very intricate process and further studies are necessary.