Brain, Mind, and the Narrative Imagination by Comer Christopher; Taggart Ashley;

Author:Comer, Christopher; Taggart, Ashley;
Language: eng
Format: epub
Publisher: Bloomsbury Publishing Plc

FIGURE 6.1 Experimental results from the search for our semantic lexicon. This shows the lateral surface of the right cerebral hemisphere. At the front (black arrow), we show a region of prefrontal cortex that responded to words describing the natural world in terms of locations, time, and navigation. Toward the rear, we show a region of parietal lobe responding to words with a mixture of social/emotional terms but also some related to time. The gray arrow becomes white where it passes out of view between the two hemispheres to denote the position of this region on the medial surface of the hemisphere. Adapted from the PrAGMATIC Brain Atlas on the Gallant Lab website https://gallantlab.org/huth2016/ (last accessed November 22, 2019). Material covered by creative commons attribution license. For related publication, see Huth, de Heer et al. (2016) Natural speech reveals the semantic maps that tile human cerebral cortex. Nature 532:453-8.

The results in Figure 6.1 show only two sample areas, each with a “word cloud” indicating words that reliably caused activity to increase in the volume making up each distinguishable cortical area. While the details here differ a little from other semantic “maps” (e.g., Binder and Desai 2011, Pulvermüller 2013, Moseley and Pulvermüller 2014), there are important points of convergence. First, large regions of both left and right hemispheres are involved. It’s only when we move away from initial linguistic processing and look at cognitive events that support narrative understanding that we see RH involvement more clearly.

Second, Huth and colleagues found that the data in their study could be naturally organized (using statistical methods) into twelve categories: some were sensory related, for example, visual and tactile, there were numeric and temporal categories, several social or emotional categories, and also an abstract category. Finally, there was a relationship between many of these categories and previously known features of cortical organization (similar to what we mentioned above from earlier studies). So, for instance, color words were found near cortical area “V4,” which is known to compute color information for visual scenes.

As a consequence of all this, and the complexity of the real narratives used, individual words could be found at more than one location. If you were to ask where the word “family” is located, the answer is: several places, depending on context. Sometimes it occurs in the vicinity of words about social relationships, but also in areas activated by words related to living spaces. This echoes our everyday distinction between denotation and connotation. Given that words are learned, and heavily cultural in origin and meaning, it was more than a little surprising that, across all of the brains analyzed, the location where particular categories were found turned out to be similar. This strongly suggests that words become anchored in cortical “neighborhoods” that are functionally related, and that both biological and cultural factors probably shape features of this atlas of meanings.

This study, along with many others, upends the oversimplification that language is a left-brain function alone. That does not change the fact that the “final common path” for speech is located in the left hemisphere.

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