Metaphors are not just ossified expressions in grammar books. Rather, they are living, evolving expressions that pepper our language far more heavily than one might think. Many expressions that we take for granted are actually metaphorical, that is, they represent one concept by referring to another. For instance, the sentence 'He was feeling down' actually involves metaphorical usage of the spatial word 'down.' Given their ubiquity, processes in the brain that mediate comprehension and production of metaphors are critically important to human language. Dr. Krishnankutty Sathian of Emory University and his colleagues are carrying out a project to determine how metaphors are processed by the brain. It turns out that metaphors very often represent a somewhat abstract concept by implicitly invoking similarity to a more concrete concept that is grounded in our sensory experiences. For example, in the sentence, 'She had a rough day,' the word 'rough' connotes something unpleasant, similar to the way a rough surface feels unpleasant. Much research has already established that various sensory domains, such as color, shape, texture and spatial location, are each processed in relatively distinct sectors of the brain (specifically, within parts known collectively as "sensory cortex"). Dr. Sathian's project is testing whether or not understanding metaphors involves activation of those particular sensory cortical regions (e.g. the region specialized for processing texture in the case of metaphorical usage of 'rough'). In order to do this, brain scans using functional magnetic resonance imaging (fMRI) are being carried out while healthy volunteers listen to sentences containing metaphors. The brain responses to metaphors are being contrasted with responses during presentation of sentences of similar difficulty but lacking metaphors. How different brain regions interact is also being examined using measures of neural connectivity. Even if the predicted sensory cortical activity is found, it does not mean that the activity is actually necessary for metaphor comprehension. To test the necessity of cortical activity, another technique known as 'transcranial magnetic' stimulation (TMS) is being used. Tiny magnetic pulses are applied to specific brain regions to transiently disrupt their function. If TMS over particular sensory cortical regions affects understanding of the corresponding metaphors, then those sensory regions are truly necessary for understanding metaphors.
This work will enable new insights into the basis of metaphorical thought. Especially because the use of metaphors in language is pervasive, this research is contributing to fundamental understanding of human cognition. This research is helping to answer the question whether comprehending metaphors requires activity, not only in classic language regions of the brain, but also more widely in other sensory regions. The findings are providing evidence concerning theories (so-called 'grounded cognition' theories), which argue that knowledge is grounded in basic sensory and motor experiences (as first theorized by Greek philosophers like Aristotle and Epicurus). The project is also showing how different brain regions, specialized for different purposes, interact during high-level thinking. This research is relevant to a variety of human activities, including literary writing, pedagogical teaching, political speeches, and product marketing, in all of which the best expositors typically make innovative and highly effective use of metaphors. It is also relevant to many neurological disorders such as autism, stroke and Alzheimer's disease, which impair communication between brain regions, resulting in problems with figurative thinking.
