THIS ARTICLE IS republished from The Conversation under a Creative Commons license.
The number of people who read for fun appears to be steadily dropping. Fifty percent of UK adults say they don’t read regularly (up from 42 percent in 2015) and almost one in four young people aged 16 to 24 say they’ve never been readers, according to research by The Reading Agency.
But what are the implications? Will people’s preference for video over text affect our brains or our evolution as a species? What kind of brain structure do good readers actually have? My new study, published in NeuroImage, has found out.
I analyzed open source data from more than 1,000 participants to discover that readers of varying abilities had distinct traits in brain anatomy.
The structure of two regions in the left hemisphere, which are crucial for language, were different in people who were good at reading.
One was the anterior part of the temporal lobe. The left temporal pole helps associate and categorize different types of meaningful information. To assemble the meaning of a word such as leg, this brain region associates the visual, sensory and motor information conveying how legs look, feel and move.
The other was Heschl’s gyrus, a fold on the upper temporal lobe which hosts the auditory cortex (the cortex is the outermost layer of the brain). Better reading ability was linked to a larger anterior part of the temporal lobe in the left hemisphere compared to the right. It makes sense that having a larger brain area dedicated to meaning makes it easier to understand words and, therefore, to read.
What might seem less intuitive is that the auditory cortex would be related to reading. Isn’t reading mainly a visual skill? Not only. To pair letters with speech sounds, we first need to be aware of the sounds of the language. This phonological awareness is a well-established precursor to children’s reading development.
A thinner left Heschl’s gyrus has previously been related to dyslexia, which involves severe reading difficulties. My research shows that this variation in cortical thickness does not draw a simple dividing line between people with or without dyslexia. Instead, it spans the larger population, in which a thicker auditory cortex correlates with more adept reading.
Why Size Matters
Is thicker always better? When it comes to cortical structure, no, not necessarily. We know the auditory cortex has more myelin in the left hemisphere of most people. Myelin is a fatty substance that acts as an insulator for nerve fibers. It increases neural communication speed and can also insulate columns of brain cells from each other. Neural columns are believed to function as small processing units.
Their increased isolation and rapid communication in the left hemisphere can be thought to enable the fast, categorical processing necessary for language. We need to know if a speaker uses the category d or t when saying dear or tear rather than detecting the exact point where the vocal folds start vibrating.