Mechanisms of aphasia recovery after stroke and the role of noninvasive brain stimulation

Abstract

One of the most frequent symptoms of unilateral stroke is aphasia, the impairment or loss of language functions. Over the past few years, behavioral and neuroimaging studies have shown that rehabilitation interventions can promote neuroplastic changes in aphasic patients that may be associated with the improvement of language functions. Following left-hemisphere strokes, the functional reorganization of language in aphasic patients has been proposed to involve both intrahemispheric interactions between damaged left-hemisphere and perilesional sites and transcallosal interhemispheric interactions between the lesioned left-hemisphere language areas and homotopic regions in the right hemisphere. A growing body of evidence for such reorganization comes from studies using transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS), two safe and noninvasive procedures that can be applied clinically to modulate cortical excitability during poststroke language recovery. We discuss a hierarchical model for the plastic changes in language representation that occur in the setting of dominant hemisphere stroke and aphasia. We further argue that TMS and tDCS are potentially promising tools for enhancing functional recovery of language and for further elucidating mechanisms of plasticity in patients with aphasia.

Effects of Noninvasive Brain Stimulation on Language Networks and Recovery in Early Poststroke Aphasia

“…Based on these pathophysiological concepts, most evidence for the effectiveness of rTMS in the literature comes from case reports, case series, and small pilot studies applying inhibitory low-frequency rTMS to right-hemispheric homotopic areas [27][28][29] (and from reviews, 2,3,7,30 ) specifically to the right pars triangularis. 14,31 In all these reported patients, a positive effect on the tested deficit was observed with the exception of one.…”

“…5,6 The effects of NBS on disturbed language networks are not yet fully understood, and various mechanisms have been postulated to explain the compensation of focal disturbances within the functional networks by excitatory or inhibitory effects on different brain regions. 5,7 The complex interaction of various ipsi-and contralateral brain regions on language function after ischemic damage to the dominant hemisphere may be modulated by NBS in different ways: excitatory stimulation to perilesional areas of the ipsilateral hemisphere 8 and inhibitory stimulation to contralateral homotopic speech areas seem to improve poststroke recovery. [9][10][11] After a feasibility study 10 indicated the possibility to recruit appropriate patients with ischemic stroke and to combine a Background and Purpose-Modulation of activity in language networks using repetitive transcranial magnetic stimulation (rTMS) may possibly support recovery from poststroke aphasia.…”

What Do Language Disorders Reveal about Brain–Language Relationships? From Classic Models to Network Approaches

“…This will require a better understanding of the mechanisms of recovery as well as the development of new therapies and neural prostheses. For instance, transcranial stimulation techniques, such as transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (Hamilton, Chrysikou, & Coslett, 2011) have been used enhance language functions in both healthy and brain-injured individuals (Marangolo et al, 2013;Naeser et al, 2005;Schlaug, Marchina, & Wan, 2011).…”

Theta Burst Stimulation Over the Right Broca's Homologue Induces Improvement of Naming in Aphasic Patients

“…4 -7 The role of the right, nondamaged hemisphere in recovery is less clear. 8,9 Some authors suggest that right-hemispheric activations early after stroke could reflect substitution of lost left-hemispheric functions. 4,10 Other authors suggest that right-hemispheric activation has a dysfunctional effect, which is explained within the framework of interhemispheric inhibition.…”