Contrasting opinions on the role of the right hemisphere in the recovery of language. A critical survey

Abstract

Background: The role of the right hemisphere (RH) in the recovery of language is quite controversial. Aims: The aim of the present survey consisted in taking into account three main models advanced to explain the reconstitution of language systems: (1) the "perilesional hypothesis," which maintains that language recovery is mainly subsumed by left hemisphere (LH) tissue adjacent to the lesion; (2) the "right hemisphere hypothesis," which assumes that restitution of language entails an increased participation of the RH; and (3) the "disinhibition hypothesis," which maintains that recovery is facilitated by disruption of inhibitions exerted by RH regions over LH language areas. Methods & Procedures: The prognostic factors in poststroke aphasia are discussed first, focusing attention on factors that could subsume an increased participation of the RH to the recovery of language. Then results obtained with techniques of noninvasive brain stimulations of the RH are taken critically into account. Outcomes & Results: As for the prognostic factors, the following points are stressed:(1) the anatomical extension of the LH lesion plays an important role both on the degree and on the path of recovery; (2) the RH structures involved in the recovery of language are generally mirror structures of the damaged LH areas; and (3) the time elapsed since the onset of aphasia influences the contribution that contralateral and ipsilesional areas give to the recovery of language. As for results obtained with techniques of noninvasive brain stimulations of the RH, this point remains controversial, because most authors support the "disinhibition hypothesis," but theoretical and factual reasons suggest caution in the interpretation of these results. Conclusions: Since the meaning of the RH activations and of results obtained with techniques of noninvasive brain stimulations remain controversial, some tentative recommendations to clarify these issues are advanced.

Neural networks for sentence comprehension and production: An ALE‐based meta‐analysis of neuroimaging studies

“…It may be that this region is engaged only in limited circumstances, as we argued above for left inferior frontal cortical regions (including the left insula), though whether these noncanonical sentences elicit activity in this region because of difficult prosody (as has been suggested for right inferior frontal cortex; Friederici, 2011) or for other reasons remains to be determined. As a second point, the engagement of this region in the comprehension of complex sentences in healthy individuals is consistent with the hypothesis that this region (and nearby and/or functionally connected regions) might be capable of contributing to the recovery of comprehension of complex sentences in individuals with agrammatic aphasia, though precisely how and to what extent is still an active area of investigation (Gainotti, 2015;Lukic et al, 2017).…”

Recovering two languages with the right hemisphere

“…Generally speaking, the plastic reorganization of the linguistic networks after a lesion requires a complex interplay between the recruitment of neurons in perilesional areas (Heiss & Graf, 1994), the modulation of existing synaptic connections, and the generation of new synapses (Tecchio et al, 2006). As highlighted in a recent critical survey on this topic (Gainotti, 2015), the role of the RH in linguistic recovery after a lesion to the LH is still controversial. Two major hypotheses have been formulated so far: the ''interhemispheric inhibition hypothesis" and the ''right hemisphere involvement hypothesis".…”

Cerebellar tDCS as a novel treatment for aphasia? Evidence from behavioral and resting-state functional connectivity data in healthy adults

“…Further, electrical field modeling requires a research quality MRI for tissue segmentation, presenting a barrier to treatment access for some people with aphasia. Targeting right hemisphere language homologs is an alternative, although the role of the right hemisphere in aphasia recovery is still hotly debated and it remains unclear whether enhancement or inhibition is the preferred strategy for right hemisphere neuromodulation (Anglade, Thiel, & Ansaldo, 2014; Gainotti, 2015; Turkeltaub, 2015). Especially with large strokes, encephalomalecia on the left may still result in unpredictable patterns of current flow when applying tDCS to the right hemisphere, especially when the “return” electrode is placed on the left side of the head, as is common in these protocols (de Aguiar et al, 2015).…”