Asyntactic comprehension, working memory, and acute ischemia in Broca’s area versus angular gyrus

Abstract

We evaluated sentence comprehension of variety of sentence constructions and components of short term memory in 53 individuals with acute ischemic stroke, to test some current hypotheses about the role of Broca's area in these tasks. We found that some patients show structure-specific, task-independent deficits in sentence comprehension, with chance level of accuracy on passive reversible sentences, more impaired comprehension of object-cleft than subject-cleft sentences, and more impaired comprehension of reversible than irreversible sentences in both sentence-picture matching and enactment tasks. In a dichotomous analysis, this pattern of “asyntactic comprehension” was associated with dysfunctional tissue in left angular gyrus, rather than dysfunctional tissue in Broca's area as previously proposed. Tissue dysfunction in left Brodmann area (BA) 44, part of Broca's area, was associated with phonological short term memory (STM) impairment defined by forward digit span ≤ 4. Verbal working memory defined by backward digit span ≤ 2 was associated with tissue dysfunction left premotor cortex (BA 6). In a continuous analysis, patients with acute ischemia in left BA 44 were impaired in phonological STM. Patients with ischemia in left BA 45 and BA 6 were impaired in passive, reversible sentences, STM, and verbal working memory. Patients with ischemia in left BA 39 were impaired in passive reversible sentences, object cleft sentences, STM, and verbal working memory. Therefore, various components of working memory seem to depend on a network of brain regions that include left angular gyrus and posterior frontal cortex (BA 6, 44, 45); left BA 45 and angular gyrus (BA 39) may have additional roles in comprehension of syntax such as thematic role checking.

Left inferior parietal lobe engagement in social cognition and language

“…Language studies have further demonstrated that stroke-induced lesions of the angular gyrus (overlapping our cluster 2) impaired processing of passive reversible sentences (e.g., “the niece was kicked by the father”) and complex object cleft constructions (e.g., “It was the niece that the father kicked”) (Newhart et al, 2011). This suggests a role of the angular gyrus in complex working memory and syntax.…”

Lesion-symptom mapping in the study of spoken language understanding

“…This is challenging from a practical standpoint, and also because there are often other factors at play early after a brain injury, such as edema and hypoperfusion, that may complicate the picture in different ways. However, several lesion-symptom mapping studies have successfully demonstrated specific regions associated with various component processes of spoken language understanding in acute stroke patients (Kümmerer et al, 2013; Newhart, Ken, Kleinman, Heidler-Gary, & Hillis 2007; Newhart et al, 2012; Race, Ochfeld, Leigh, & Hillis, 2012; Rogalsky, Pitz, Hillis, & Hickok, 2008; Tsapkini, Frangakis, & Hillis, 2011) or resective surgery patients in the immediate post-operative period (Wilson et al, 2015). …”

“…The most commonly implicated regions have been left inferior frontal cortex, left superior temporal cortex, and left inferior parietal cortex, with many studies reporting one or more of these regions to be implicated in sentence-level comprehension (Amici et al, 2007; Dronkers, Wilkins, Van Valin, Redfern, & Jaeger, 2004; Fridriksson, Fillmore, Guo, & Rorden, 2015; Leff et al, 2009; Newhart et al, 2012; Rogalski et al, 2011; Teichmann et al, 2015; Thothathiri, Kimberg, & Schwartz, 2012; Wilson et al, 2011; Wilson, Galantucci, Tartaglia, & Gorno-Tempini, 2012). Some studies have suggested that specific regions within this network have specific functions, such as a role for inferior frontal cortex in processing syntactically complex sentences (Amici et al, 2007), and a role for the posterior superior temporal gyrus in auditory short-term memory in support of sentence comprehension (Leff et al, 2009; Wilson, Galantucci, Tartaglia, & Gorno-Tempini, 2012).…”

Deficit-lesion correlations in syntactic comprehension in aphasia

“…Newhart et al (2012) studied 53 PWA with strokes on their first hospitalization day. They measured the size of infarction and hypoperfusion in Broca’s area (BA 44 and 45) and 12 other BAs (6, 10, 11,18, 19, 20, 21, 22, 37, 38, 39, 40) on a three point scale: (1) part, (2) all, or (0) none.…”