Adaptive significance of right hemisphere activation in aphasic language comprehension

Abstract

Aphasic patients often exhibit increased right hemisphere activity during language tasks. This may represent takeover of function by regions homologous to the left-hemisphere language networks, maladaptive interference, or adaptation of alternate compensatory strategies. To distinguish between these accounts, we tested language comprehension in 25 aphasic patients using an online sentence-picture matching paradigm while measuring brain activation with MEG. Linguistic conditions included semantically irreversible (“The boy is eating the apple”) and reversible (“The boy is pushing the girl”) sentences at three levels of syntactic complexity. As expected, patients performed well above chance on irreversible sentences, and at chance on reversible sentences of high complexity. Comprehension of reversible non-complex sentences ranged from nearly perfect to chance, and was highly correlated with offline measures of language comprehension. Lesion analysis revealed that comprehension deficits for reversible sentences were predicted by damage to the left temporal lobe. Although aphasic patients activated homologous areas in the right temporal lobe, such activation was not correlated with comprehension performance. Rather, patients with better comprehension exhibited increased activity in dorsal fronto-parietal regions. Correlations between performance and dorsal network activity occurred bilaterally during perception of sentences, and in the right hemisphere during a post-sentence memory delay. These results suggest that effortful reprocessing of perceived sentences in short-term memory can support improved comprehension in aphasia, and that strategic recruitment of alternative networks, rather than homologous takeover, may account for some findings of right hemisphere language activation in aphasia.

Neuroplasticity of language in left‐hemisphere stroke: Evidence linking subsecond electrophysiology and structural connections

“…We note, however, that the study was conducted on a welldelineated target population with lesions consistently affecting the temporal lobe and, in particular, the middle temporal gryus. Although previous studies examining oscillations included more patients, the lesion overlap in the temporal lobe in those studies may not have exceeded the overlap in our sample of six patients [e.g., Kielar et al, 2016;Meltzer et al, 2013;Spironelli and Angrilli, 2009;Spironelli et al, 2013]. Moreover, we took advantage of the heterogeneity and performed individual-participant statistical analyses to be able to explain the patterns of brainbehavior relationships observed.…”

“…Similarly, neuroplasticity indexed by spectral and evoked potential changes in working memory and attention has been observed after strokes in lateral frontal cortex (Voytek et al 2010). The potential of such neuronal oscillations as biomarkers for monitoring neurorehabilitation and recovery of language function is largely unexplored (e.g., Kielar et al 2016; Meltzer et al 2013; Nicolo et al, 2015; Spironelli & Angrilli, 2009; Spironelli et al 2013). …”

The canonical semantic network supports residual language function in chronic post‐stroke aphasia

“…This is somewhat surprising given that the use of statistical controls to reduce confounds related to lesion volume effects is relatively common in lesion-symptom mapping research [Rorden and Karnath, 2004; Schwartz et al, 2009; Zhang et al, 2014]. The logic behind using statistical controls to account for lesion volume effects is that since (1) larger lesions are often associated with more severe impairments [Allendorfer et al, 2012; Butler et al, 2014; Cheng et al, 2014; Karnath et al, 2004; Kümmerer et al, 2013; Meltzer et al, 2013; van Oers et al, 2010; Rorden and Karnath, 2004; Szaflarski et al, 2013; Yarnell et al, 1976], and (2) larger lesions have a higher probability of including both task-relevant and task-irrelevant voxels [Karnath et al, 2004; Rorden and Karnath, 2004; Schwartz et al, 2009; Zhang et al, 2014], lesion volume effects have the potential to introduce bias into measurements of lesion-behavior relationships at voxels that are primarily damaged in patients with large lesions [Karnath et al, 2004; Zhang et al, 2014]. In functional neuroimaging, the probability that a voxel is active during task performance depends on the probability that the tissue at that voxel is spared, and the probability that the tissue at a given voxel in the left hemisphere is spared depends on the size of the lesion.…”

Behavioural and neuroimaging changes after naming therapy for semantic variant primary progressive aphasia

“…In functional neuroimaging studies, individuals with chronic aphasia caused by left-hemisphere stroke often show increased neural activity in perilesional regions around the location of the lesion; increased recruitment is also found in the contralesional areas in the right hemisphere, including regions homologous to the left hemisphere language areas (Breier et al 2007;Meinzer et al 2007, Thompson, 2010Vitali et al 2007). Although activation of left hemisphere regions has been associated with the best language recovery (Cornelissen et al 2003;Heiss et al 1999;Heiss and Thiel, 2006;Léger et al 2002;Vitali et al 2007), there is also evidence suggesting that right hemisphere activation represents adaptive plasticity or compensatory mechanisms, as new or homologous right hemisphere regions appear to take over functions of the damaged left hemisphere (Blasi et al 2002;Meltzer et al 2013;Musso et al 1999;Thulborn et al 1999). Both left and right hemisphere regions may contribute to language recovery, but in a slightly different manner (Brieier et al 2007(Brieier et al , 2009Crinion and Leff, 2007;Fridriksson et al 2006;Meinzer and Breitenstein, 2008;Meinzer et al 2007).…”