The relationships between the amount of spared tissue, percent signal change, and accuracy in semantic processing in aphasia

Abstract

Recovery from aphasia, loss of language following a cerebrovascular incident (stroke), is a complex process involving both left and right hemispheric regions. In our study, we analyzed the relationships between semantic processing behavioral data, lesion size and location, and functional percent signal change from functional magnetic resonance imaging (fMRI) data. This study included 14 persons with aphasia in the chronic stage of recovery (six or more months post stroke) and eight healthy controls who performed semantic processing tasks of determining whether a written semantic feature matched a picture or whether two written words were related or not. Using region of interest (ROI) analysis, we found that percent signal change in left inferior frontal gyrus pars opercularis and pars triangularis, despite significant damage, were the only regions to correlate with behavioral accuracy. Additionally, the more the damage to LIFG, LMTG and AG/SMG, the higher the percent signal change in bilateral superior frontal gyrus, middle frontal gyrus, and anterior cingulate, suggesting that these regions appear to serve as an assistive network in the case of damage to traditional language regions. Relative to controls who showed mainly positive correlations in activation between and within LH and RH ROIs, patients showed positive and negative correlations. Specifically, the right inferior frontal gyrus pars orbitalis is presumed to serve a monitoring function. These results reinforce the importance of the left hemisphere in language processing in aphasia, and provide a framework for the relative importance of left and right language regions in the brain.

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

“…Hartwigsen et al, 2013]. While previous studies have investigated how activity in the right hemisphere relates to the effects of damage to specific left hemispheric regions [Blank et al, 2003; Sims et al, 2016; Turkeltaub et al, 2011], we are not aware of any studies that have directly measured how the activation in the right hemisphere relates to the extent of damage sustained by the left hemisphere.…”

Linking left hemispheric tissue preservation to fMRI language task activation in chronic stroke patients

“…If canonical language networks are not recoverable, then compensation via un-damaged right hemispheric areas is thought to underlie residual language abilities (Forkel et al, 2014; Hamilton et al, 2011; Heiss and Thiel, 2006; Saur and Hartwigsen, 2012; Turkeltaub et al, 2011). The nature of compensation afforded by right hemispheric regions is poorly understood, but recent evidence suggests that it is likely more complex than a simple take-over of the damaged areas by right hemispheric homologues (Griffis et al, 2017b; Sims et al, 2016; Laura M Skipper-Kallal et al, 2017; Laura M. Skipper-Kallal et al, 2017; Turkeltaub et al, 2012), and that it may depend on factors such as the pre-existing structural properties of the right hemisphere (Forkel et al, 2014) and the stage of recovery (Heiss and Thiel et al, 2006; Bartolomeo and de Schotten, 2016). Further, although extensive left hemispheric damage might be expected to result in prolonged dysfunction in canonical language networks (Heiss and Thiel, 2006), this may not always be the case (Griffis et al, 2017b).…”

“…While most such studies have compared task-evoked activation between groups with vs. without damage to a target brain region(s) (Blank et al, 2003; Blasi et al, 2002; Heiss et al, 1999; Specht et al, 2009; Turkeltaub et al, 2011), some recent studies have used less constrained approaches that include lesion-symptom mapping of task activation (Fridriksson et al, 2010; Skipper-Kallal et al, 2017b), correlating regional activation with measures of tissue preservation/damage (Griffis et al, 2017b; Sims et al, 2016; Skipper-Kallal et al, 2017a), and joint independent component analysis of lesion and activation data (Abel et al, 2015; Specht et al, 2009). While only a minority of this work has focused on how activity in preserved left hemispheric areas relates to brain structure, the recruitment of perilesional areas during naming tasks has been previously suggested to depend on the preservation of left inferior frontal cortex (Fridriksson et al 2010).…”

“…While only a minority of this work has focused on how activity in preserved left hemispheric areas relates to brain structure, the recruitment of perilesional areas during naming tasks has been previously suggested to depend on the preservation of left inferior frontal cortex (Fridriksson et al 2010). More recently, language task-evoked activation in the left middle/superior frontal gyri and anterior cingulate cortex was reported to negatively correlate with the amount of spared tissue in posterior language areas (Sims et al, 2016). While several studies have found evidence for increased task-evoked activity in right hemispheric homologues of damaged cortical areas (Blank et al, 2003; Blasi et al, 2002; Heiss et al, 1999; Specht et al, 2009; Turkeltaub et al, 2011), increases in activation have been reported in other areas as well (Heiss et al, 1999; Sims et al, 2016; Skipper-Kallal et al, 2017b; Specht et al, 2009), and a recent study reported decreased naming-related activation in right hemispheric homologues of damaged pre-frontal areas (Skipper-Kallal et al, 2017a).…”

“…A lack of consensus among previous studies may stem in part from common limitations such as small sample sizes (i.e. n =7–15 per group) (Abel et al, 2015; Blank et al, 2003; Blasi et al, 2002; Fridriksson et al, 2010; Heiss et al, 1999; Robson et al, 2016; Sims et al, 2016; Specht et al, 2009), the lack of controls for potential confounding effects of lesion size on structure-function relationships (Abel et al, 2015; Blank et al, 2003; Blasi et al, 2002; Heiss et al, 1999; Robson et al, 2016; Specht et al, 2009; Turkeltaub et al, 2011), and differences in the type of task employed, among other factors.…”