Noninvasive brain stimulation in the treatment of aphasia: Exploring interhemispheric relationships and their implications for neurorehabilitation

Abstract

Aphasia is a common consequence of unilateral stroke, typically involving perisylvian regions of the left hemisphere. The course of recovery from aphasia after stroke is variable, and relies on the emergence of neuroplastic changes in language networks. Recent evidence suggests that rehabilitation interventions may facilitate these changes. Functional reorganization of language networks following left-hemisphere stroke and aphasia has been proposed to involve multiple mechanisms, including intrahemispheric recruitment of perilesional left-hemisphere regions and transcallosal interhemispheric interactions between lesioned left-hemisphere language areas and homologous regions in the right hemisphere. Moreover, it is debated whether interhemispheric interactions are beneficial or deleterious to recovering language networks. Transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) are two safe and noninvasive procedures that can be applied clinically to modulate cortical excitability during poststroke language recovery. Intervention with these noninvasive brain stimulation techniques also allows for inferences to be made regarding mechanisms of recovery, including the role of intrahemispheric and interhemispheric interactions. Here we review recent evidence that suggests that TMS and tDCS are promising tools for facilitating language recovery in aphasic patients, and examine evidence that indicates that both right and left hemisphere mechanisms of plasticity are instrumental in aphasia recovery.

Phase-Amplitude Coupling of Neural Oscillations can be Effectively Probed with Concurrent TMS-EEG

“…Due to its extensive effects on human perception, cognition and action, transcranial magnetic stimulation (TMS) is nowadays widely used in both basic neuroscientific research (e.g., during investigations of visual awareness [1], attention [2], speech [3] and motor processing [4]) and in clinical practice (with potential treatment domains [see guidelines on therapeutic use [5]] including medication-resistant major depressive disorder [6], post-stroke motor impairment [7], aphasia [8] and schizophrenia [9]). Despite this broad scope of application, knowledge of the precise neurophysiological effects of TMS is still incomplete.…”

Treatment for Lexical Retrieval Impairments in Primary Progressive Aphasia: A Research Update with Implications for Clinical Practice

“…At high frequencies (above 5 Hz), this induces action potentials in the underlying cortical and white matter neurons, with potentially longlasting effects on neuronal excitability. 66,67 All five studies that investigated lexical retrieval following rTMS in PPA 13,64,[67][68][69] stimulated the left (and in one case, also the right) dorsolateral prefrontal cortex. They reported improvements in tasks including verb production, word generation, paragraph writing, and action naming in participants with nf/avPPA, and the effects were relatively short lived (back to baseline at 1 week retest in one study and 3 months in another).…”

“…65 In tDCS, a small current (1-2 mA) applied to the scalp via two surface electrodes modulates neuronal excitability without directly inducing action potentials. 66 Anodal tDCS, in which the current runs from the positive to the negative electrode, has an excitatory effect which is enhanced when combined with behavioral treatment activities. 70 A range of montages (relative positioning of anodal and cathodal electrodes) combined with a range of behavioral treatments or other language activities have been used.…”

Estimulación eléctrica por corriente continua en el tratamiento de la afasia

“…Otra limitación son los efectos secunda rios, la mayoría de ellos derivados de la aplicación de pequeñas descargas eléctricas sobre el cuero ca belludo. Estos efectos son leves y claramente meno res que los causados, por ejemplo, en la estimulación magnética transcraneal o en la estimulación eléc trica intracraneal [21,22]. Entre los más frecuentes se encuentran la picazón (39,3%) y el cosquilleo/ hormigueo (22,2%), seguidos por el dolor de cabeza (14,8%), el malestar (10,4%) y la sensación de que mazón en la zona estimulada (8,7%) [23].…”