Your brain can read the lines, and it can read between the lines, but it does both using the same neurons.

Image credits Chepe Nicoli.

While we can consciously tell when a word is being used literally or metaphorically, our brains process it just the same. The findings come from a new study by University of Arizona researcher Vicky Lai, which builds on previous research by looking at when, exactly, different regions of the brain are activated in metaphor comprehension.

Twisting our words

“Understanding how the brain approaches the complexity of language allows us to begin to test how complex language impacts other aspects of cognition,” she said.

People use metaphors all the time. On average, we sneak one in once every 20 words, says Lai, an assistant professor of psychology and cognitive science at the UA. As director of the Cognitive Neuroscience of Language Laboratory in the UA Department of Psychology, she is interested in how the brain distinguishes metaphors from the broad family of language, and how it processes them.

Previous research has hinted that our ability to understand metaphors may be rooted in bodily experiences. Functional brain imaging studies (fMRI), for example, have indicated that hearing a metaphor such as “a rough day” activates regions of the brain associated with the sense of touch. Hearing that someone is “sweet”, meanwhile, activates taste areas, whereas “grasping a concept” lights up brain regions involved in motor perception and planning are activated.

In order to get to the bottom of things, Lai used EEG (electroencephalography) to record the electrical patterns in the brains of participants who were presented with metaphors that contained action words — like “grasp the idea” or “bend the rules.” The participants were shown three different sentences on a computer screen, presented one word at a time. One of these sentences described a concrete action — “The bodyguard bent the rod.” Another was a metaphor using the same verb — “The church bent the rules.” The third sentence replaced the verb with a more abstract word that kept the metaphor’s meaning — “The church altered the rules.”

Seeing the world “bent” elicited a similar response in participants’ brains whether it was used literally or metaphorically. Their sensory-motor region activated almost immediately — within 200 milliseconds — of the verb appearing on screen. A different response, however, was elicited when “bent” was replaced with “altered.”

Lai says her work supports previous findings from fMRI (functional magnetic resonance imaging) studies. However, while fMRI measures blood flow in the brain as a proxy for neural activity, the EEG measures electrical activity directly. Thus, it provides a clearer picture of the role sensory-motor regions of the brain play in metaphor comprehension, she explains.

“In an fMRI, it takes time for oxygenation and deoxygenation of blood to reflect change caused by the language that was just uttered,” Lai said. “But language comprehension is fast — at the rate of four words per second.”

“By using the brainwave measure, we tease apart the time course of what happens first,” Lai said.

While an fMRI won’t show you exactly which brain region is working to decipher an action-based metaphor (because it won’t show you which region activates immediately and which does so after we already understand the metaphor), the EEG provides a much more precise sense of timing. The near-immediate activation of sensory-motor areas after the verb was displayed suggests that these areas of the brain are key to metaphor comprehension.

Lai recently presented ongoing research looking into how metaphors can aid learning and retention of science concepts at the annual meeting of the Cognitive Neuroscience Society in San Francisco. She hopes the study we’ve discussed today will help her lab better understand how humans comprehend language and serve as a base for her ongoing and future research.

The paper “Concrete processing of action metaphors: Evidence from ERP” has been published in the journal Brain Research.