Non-invasive Brain Stimulation in the Treatment of Post-stroke and Neurodegenerative Aphasia: Parallels, Differences, and Lessons Learned

Abstract

Numerous studies over the span of more than a decade have shown that non-invasive brain stimulation (NIBS) techniques, namely transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS), can facilitate language recovery for patients who have suffered from aphasia due to stroke. While stroke is the most common etiology of aphasia, neurodegenerative causes of language impairment—collectively termed primary progressive aphasia (PPA)—are increasingly being recognized as important clinical phenotypes in dementia. Very limited data now suggest that (NIBS) may have some benefit in treating PPAs. However, before applying the same approaches to patients with PPA as have previously been pursued in patients with post-stroke aphasia, it will be important for investigators to consider key similarities and differences between these aphasia etiologies that is likely to inform successful approaches to stimulation. While both post-stroke aphasia and the PPAs have clear overlaps in their clinical phenomenology, the mechanisms of injury and theorized neuroplastic changes associated with the two etiologies are notably different. Importantly, theories of plasticity in post-stroke aphasia are largely predicated on the notion that regions of the brain that had previously been uninvolved in language processing may take on new compensatory roles. PPAs, however, are characterized by slow distributed degeneration of cellular units within the language system; compensatory recruitment of brain regions to subserve language is not currently understood to be an important aspect of the condition. This review will survey differences in the mechanisms of language representation between the two etiologies of aphasia and evaluate properties that may define and limit the success of different neuromodulation approaches for these two disorders.

Primer Progressive Aphasia with Psychiatric Symptoms

“…Indeed, our patient used acetylcholine esterase inhibitors but experienced no progress. It has been put forth as a result of the case presentations in recent years that TMS is partially useful in PPA cases [11,12]. Controlled studies that will be carried out in this area will put forth the effectiveness of TMS better.…”

Cortical waves and post‐stroke brain stimulation

“…The first reason is that the focus of research has progressively shifted from examining specific brain regions to exploring specific brain networks. () The challenge to treat brain networks is to understand and control the brain's capacity to reorganize itself . The second reason is that it is now possible to describe cortical waves mathematically with increasing precision.…”

“…This growing interest is probably due in part to an increasing understanding of the physiological control mechanisms driving normal and abnormal structural and functional brain reorganization. Specifically, these mechanisms are actively explored for stroke [3][4][5] and for post stroke aphasia, 6,7 to name a few. Recent studies on detailed mapping of the healthy and diseased brain connectivity shed new light on the relation between brain structure and function.…”

“…31,32 The challenge to treat brain networks is to understand and control the brain's capacity to reorganize itself. 7 The second reason is that it is now possible to describe cortical waves mathematically with increasing precision. 10,33,34 These recent modeling studies are opening the possibility to harness the brain's capacity to reorganize itself with the help of an outside stimulation introduced only when and where necessary.…”

Estimulação transcraniana por corrente contínua: estudo sobre respostas em tarefas de nomeação em afásicos

“…Studies of tDCS effects, with or without concomitant speech therapy, can clarify neurophysiological and rehabilitation aspects in aphasia. In this sense, the authors (5)(6)(7)(8)(9) recommend tDCS as an adjunct to speech therapy for aphasia due to its therapeutic effects, even when low intensity current is applied, because it can be observed a transient modification in the neural network resulting in the modulation of brain activity that causes local cortical excitability and synaptic alterations (10) . Investigations also confirmed improvements in linguistic abilities associated with gestural communication (11) and vocabulary acquisition (12) .…”