The right hemisphere is not unitary in its role in aphasia recovery

Abstract

Neurologists and aphasiologists have debated for over a century whether right hemisphere recruitment facilitates or impedes recovery from aphasia. Here we present a well-characterized patient with sequential left and right hemisphere strokes whose case substantially informs this debate. A 72-year-old woman with chronic nonfluent aphasia was enrolled in a trial of transcranial magnetic stimulation (TMS). She underwent 10 daily sessions of inhibitory TMS to the right pars triangularis. Brain activity was measured during picture naming using fMRI prior to TMS exposure and before and after TMS on the first day of treatment. Language and cognition were tested behaviorally three times prior to treatment, and at 2 and 6 months afterwards. Inhibitory TMS to the right pars triangularis induced immediate improvement in naming, which was sustained 2 months later. FMRI confirmed a local reduction in activity at the TMS target, without expected increased activity in corresponding left hemisphere areas. Three months after TMS, the patient suffered a right hemisphere ischemic stroke, resulting in worsening of aphasia without other clinical deficits. Behavioral testing 3 months later confirmed that language function was impacted more than other cognitive domains. The paradoxical effects of inhibitory TMS and the stroke to the right hemisphere demonstrate that even within a single patient, involvement of some right hemisphere areas may support recovery, while others interfere. The behavioral evidence confirms that compensatory reorganization occurred within the right hemisphere after the original stroke. No support is found for interhemispheric inhibition, the theoretical framework on which most therapeutic brain stimulation protocols for aphasia are based.

Neuroplasticity in the language system: Reorganization in post-stroke aphasia and in neuromodulation interventions

“…By some accounts, the right hemisphere plays a largely compensatory role in the reacquisition of language abilities in persons with aphasia. This is supported by lesion studies that have shown that secondary injury to right perisylvian structures can reverse improvements in language performance experienced by patients with prior left hemisphere lesions (Barlow, 1877;Turkeltaub et al, 2012), as well as by more recent studies that have shown that the integrity of right hemisphere structures is associated with improved language recovery (Xing et al, 2016;Pani et al, 2016). In this issue of RNN, work by Zheng and colleagues (2016) builds upon and extends ideas based on this model.…”

“…In this special issue of RNN, Heiss (2016) presents PET data demonstrating that inhibitory repetitive TMS (rTMS) of the right inferior frontal gyrus results in both clinical improvement in aphasia and a shift from right to left hemisphere activation. Other work has suggested that the role of the right hemisphere in aphasia recovery is not monolithic, that different patients may employ different language recovery mechanisms, and that multiple recovery mechanisms may even be employed within the same individual (Turkeltaub 2012).…”

Dynamics of functional MRI and speech function in patients after resection of frontal and temporal lobe tumors

“…На этом основано применение инактивации гомоло-гичных речевым зонам левого полушария отделов правого полушария с помощью ТМС у больных с речевыми расстройствами для восстановления функции речи [32,33]. Как считают A. Thiel и соавт.…”

Neuroimagen funcional y lenguaje

“…En segundo lugar, que una persistencia temporal de la activación funcional de la corteza frontal derecha durante la ejecución en tareas de lenguaje en estadios evolucionados de una afasia impide una mayor recuperación de los déficits lingüísticos. Ello pueda explicarse, probablemente, al dificultar que las áreas lingüísticas del hemisferio izquierdo preservadas puedan implicarse en la reorganización funcional del lenguaje perdido [22][23][24] .…”