Fronto-parietal network supports context-dependent speech comprehension

Abstract

Knowing the context of a discourse is an essential prerequisite for comprehension. Here we used functional magnetic resonance imaging (fMRI) to disclose brain networks supporting context-dependent speech comprehension. During fMRI, 20 participants listened to 1-min spoken narratives preceded by pictures that were either contextually matching or mismatching with the narrative. Matching pictures increased narrative comprehension, decreased hemodynamic activity in Broca׳s area, and enhanced its functional connectivity with left anterior superior frontal gyrus, bilateral inferior parietal cortex, as well as anterior and posterior cingulate cortex. Further, the anterior (BA 45) and posterior (BA 44) portions of Broca׳s area differed in their functional connectivity patterns. Both BA 44 and BA 45 have shown increased connectivity with right angular gyrus and supramarginal gyrus. Whereas BA 44 showed increased connectivity with left angular gyrus, left inferior/middle temporal gyrus and left postcentral gyrus, BA 45 showed increased connectivity with right posterior cingulate cortex, right anterior inferior frontal gyrus, lateral occipital cortex and anterior cingulate cortex. Our results suggest that a fronto-parietal functional network supports context-dependent narrative comprehension, and that Broca׳s area is involved in resolving ambiguity from speech when appropriate contextual cues are lacking.

Keywords: Broca׳s area; Functional connectivity; ISC; Narrative; PPI; Speech comprehension; Wernicke׳s area; fMRI.

Fig. 1

Sample trials with matching (top) and mismatching (bottom) contextual cues. Narratives described complex action sequences such as fishing in general terms that were ambiguous without the contextual cues. Before each narrative, participants saw a contextually matching or mismatching visual cue.

Fig. 2

Means and standard errors of means for comprehension (left) and recall (right) ratings.

Fig. 3

(A) and (B) Brain regions showing increased activity (cold colours) for narratives presented in mismatching versus matching context, and enhanced functional connectivity (hot colours) for narratives presented in matching versus mismatching context. Seed region in Broca׳s area for connectivity analysis is denoted by the red circle in the volume renders. Data are thresholded at Z>2.3, and FDR corrected (p<0.05) at the cluster level. (C) Mean signal percentage change plot shows averages for BA 44 and BA 45 seeds. Error bars show standard error of the mean.

Fig. 4

(A) and (B) Brain regions showing significant functional connectivity with posterior (hot colours) and anterior (cold colours) Broca׳s area (seeds indicated by orange and blue circles respectively) during matching versus mismatching trials. Overlap is indicated in purple. Connectivity from both seeds increases only in the right inferior parietal cortex (AG/SMG, indicated by purple). Data are thresholded at Z>2.3, and FDR corrected (p<0.05) at the cluster level.

Fig. 5

Brain regions where ISC was modulated by contextual cues. Hot colours denote regions where ISC was significantly higher for contextually mismatching trials. The only area where ISC was higher in contextually matching trials was Crus II of cerebellum (in blue). Data are thresholded at cluster significance threshold of p<0.01.