Broca's area, sentence comprehension, and working memory: an fMRI Study - PubMed (original) (raw)

Broca's area, sentence comprehension, and working memory: an fMRI Study

Corianne Rogalsky et al. Front Hum Neurosci. 2008.

Abstract

The role of Broca's area in sentence processing remains controversial. According to one view, Broca's area is involved in processing a subcomponent of syntactic processing. Another view holds that it contributes to sentence processing via verbal working memory. Sub-regions of Broca's area have been identified that are more active during the processing of complex (object-relative clause) sentences compared to simple (subject-relative clause) sentences. The present study aimed to determine if this complexity effect can be accounted for in terms of the articulatory rehearsal component of verbal working memory. In a behavioral experiment, subjects were asked to comprehend sentences during concurrent speech articulation which minimizes articulatory rehearsal as a resource for sentence comprehension. A finger-tapping task was used as a control concurrent task. Only the object-relative clause sentences were more difficult to comprehend during speech articulation than during the manual task, showing that articulatory rehearsal does contribute to sentence processing. A second experiment used fMRI to document the brain regions underlying this effect. Subjects judged the plausibility of sentences during speech articulation, a finger-tapping task, or without a concurrent task. In the absence of a secondary task, Broca's area (pars triangularis and pars opercularis) demonstrated an increase in activity as a function of syntactic complexity. However, during concurrent speech articulation (but not finger-tapping) this complexity effect was eliminated in the pars opercularis suggesting that this region supports sentence comprehension via its role in articulatory rehearsal. Activity in the pars triangularis was modulated by the finger-tapping task, but not the speech articulation task.

Keywords: Broca's area; fMRI; language; syntax; working memory.

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Figures

Figure 1

Figure 1

Schematic of behavioral task paradigm with SOAP stimuli (Love and Oster, 2002). Note that the concurrent task condition was employed during both the initial perception and processing of the sentence, as well as during the post-processing matching task.

Figure 2

Figure 2

Mean comprehension performance as a function of sentence type and concurrent task. Note that during each concurrent task, 10 of each sentence type were presented. Error bars represent 95% confidence intervals.

Figure 3

Figure 3

Plausibility judgment performance for each sentence type in each concurrent task condition. Mean a′ values across subjects for each sentence type in each task condition are depicted. Error bars represent 95% confidence intervals.

Figure 4

Figure 4

Regions active across subjects during the performance of both tasks and each task, respectively, in the absence of sentence presentation, compared to rest (p < 0.005).

Figure 5

Figure 5

Left inferior frontal voxel clusters more active during the presentation of object-relative clause sentences than subject-relative clause sentences (p < 0.005). Clusters shown are those meeting these criteria while subjects were performing (A) no secondary task, (B) articulation, or (C) a finger-tapping task. Talairach coordinates for peak activity in each cluster are listed.

Figure 6

Figure 6

Conjunction of regions active during articulation alone (p < 0.005) and regions more active during object-relative than subject-relative sentences during no secondary task (p < 0.005). The crosshairs converge on the largest voxel meeting these criteria (left pars opercularis, −42 12 25).

Figure 7

Figure 7

Mean peak amplitudes of the left pars opercularis (A) and left pars triangularis (B) regions more active during the perception of object-relative sentences than during subject-relative sentences (p < 0.005) in the absence of a secondary task, or during one of the concurrent tasks, averaged across trials and subjects. Mean peak amplitudes of each cluster are shown for each sentence type presented during each task condition, as well as for just articulation and finger-tapping alone. Error bars represent 95% confidence intervals. The Talairach coordinates of each cluster's peak are given, and correspond to the contrast maps in Figure 5.

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