Three cerebral networks integrate linguistic information with global and local contextual cues

Outside of the laboratory settings one rarely encounters situations where one would have to try to understand discourse without contextual information. When those instances do take place, it is often difficult to comprehend until one gets clues on the relevant context; on the other hand, with the appropriate context provided, it is often very easy to predict what another is about to say, even if the information that is provided per se would be rather limited. The contextual cues can further be broken down to local and global; when listening to narrated stories or discourse, the one or two preceding sentences are though to provide the local context, whereas the preceding paragraph typically is thought to provide the global context that guides comprehension. The underlying neural mechanisms have, however, remained largely unexplored, with some cognitive theories speculating that availability of local and global contextual information in working memory would be the determining factor.

In their recent study Egidi and Caramazza (2013) probed, by combining behavioral measures and functional magnetic resonance imaging in healthy volunteers, the neural structures supporting integration of narrative information by local and global contextual information. They specifically used short stories where the endings were consistent vs. inconsistent with the global vs. local context, set up by distally vs. proximally preceding sentences. Thirty subjects first participated in a self-paced reading task where they were instructed to move to the next sentence only when they had comprehended the one at hand. The subjects read locally consistent sentences quicker, but slower when the sentences were globally inconsistent, and vice versa, thus demonstrating robust behavioral interaction effects. Fourteen subjects took part in the functional magnetic resonance imaging study that disclosed involvement of three different networks of brain areas, one comprising superior parietal areas and intraparietal sulcus associated with integration of story endings with both local and global contextual information, one that consisted of supramarginal gyrus, superior parietal lobule, and anterior intraparietal sulcus sensitive to availability of global context, and a third one comprising  of multiple areas that was associated with fluency of the processing given the local context. 

These results are highly exciting in that they illuminate how global and immediate/local contextual information is integrated by the brain to facilitate comprehension. The setup and findings of the authors provide interesting possibilities for further neuroimaging research on this very important topic that is one of the most fundamental research questions concerning human language comprehension. After all, language comprehension is a process that to a large degree relies on (and in case of misinterpretations is biased by) preceding contextual information. Understanding the underlying neural mechanism provides important insights as to how contextually-driven language comprehension is possible.

Reference: Egidi G, Caramazza A. Cortical systems for local and global integration in discourse comprehension, NeuroImage (2013), advance online publication prior to print. http://dx.doi.org/10.1016/j.neuroimage.2013.01.003

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