Are you a great reader? Your brain may have a different structure than the rest

This article was originally published in The Conversation under a Creative Commons license.

The number of people who read for fun seems to be steadily declining. According to The Reading Agency, 50% of British adults say they do not read regularly, up from 42% in 2015; and almost one in four young people between 16 and 24 years old claim to have never been readers. Are there any implications? Does people’s preference for videos over text affect our brain or our evolution? My study published in the journal NeuroImagine answers these questions.

What brain regions influence reading?

I analyzed open source data from more than 1,000 participants to find that readers of varying abilities had distinctive features in brain anatomy. The structure of two regions of the left hemisphere, crucial for language, was different in people who were “good readers.” One of them is the anterior part of temporal lobe; The left pole helps associate and categorize different types of meaningful information. To assemble the meaning of a word like ‘leg’, this region associates the visual, sensory and motor information that conveys the look, feel and movement of the legs.

The other was the Heschl’s gyrus: a fold of the superior temporal lobe that houses the auditory cortexthat is, the outer layer of the brain. Better reading ability was related 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 specialized in meaning makes it easier to understand words, and therefore, reading.

What may seem less intuitive is that the auditory cortex is related to reading. Isn’t reading supposed to be a visual skill? Yes, but it doesn’t just require our eyes. To match letters to speech sounds, we first have to be aware of the sounds of the language. This phonological awareness is a precursor to reading development in children. Previously, a thinner left Heschl’s gyrus was linked to dyslexia, which involves severe reading difficulties. My research demonstrates that variation in cortical thickness does not draw a simple dividing line between people with and without dyslexia; On the contrary, it covers the general population, in which thicker auditory cortex correlates with more skilled reading.

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Does cortex size matter?

When it comes to cortical structure no, not necessarily. We know that 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 the speed of neuronal communication and can also isolate columns of brain cells from each other. Neural columns are thought to function as small processing units, and their greater isolation combined with rapid communication in the left hemisphere allows for the categorical processing necessary for language.

For example, we need to know whether a speaker uses the category ‘d’ or ‘t’ when saying ‘dear’ (dear) or ‘tear’ (tear), instead of detecting the exact point at which the vocal cords they start to vibrate. According to the “balloon model” of cortical growth, increased myelin squeezes the cortical areas of the left hemisphere, making them flatter but more extended. Thus, although the left auditory cortex is thicker in “good readers”, it is still thinner and much more extended than the right cortex. This hypothesis was corroborated in recent research, where the left hemisphere presented larger but thinner cortical areas with a higher degree of myelin.