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And it is largely due to… sound, and the awareness of sounds in the language in which we read.
The number of people who read for fun appears to be steadily decreasing. Among the British, 50% say they do not read regularlycompared to 42% in 2015, and almost one in four young people aged between 16 and 24 say they have never been a reader, according to a July report from The Reading Agency.
But what are the implications? Will people’s preference for video over text affect our brain or our evolution as a species? What type of brain structure do good readers actually have?
The phonetics teacher Mikael Roll analyzed data from more than 1000 participants to discover that readers with different abilities have different characteristics in the anatomy of the brain. According to his study in Neuroimage, the structure of two regions of the left hemisphere crucial to language were different in people who were good at reading.
One of them, the anterior part of the temporal lobe. The left temporal pole helps associate and categorize different types of information with meaning. To bring together the meaning of a word like leg, this brain region combines visual, sensory and motor information that conveys the look, feel and movement of the legs.
The other was Heschl’s gyrus, a fold in the superior temporal lobe that houses the auditory cortex (the cortex is the outermost layer of the brain). Better reading ability was associated with a larger anterior portion 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, consequently, read.
Reading is not just with your eyes
What may seem less intuitive is that the auditory cortex is related to reading. Isn’t reading primarily a visual skill? Not only. To associate letters with speech sounds, We must first be aware of the sounds of the language. This phonological awareness is a well-established precursor to reading development in children.
A thinner left Heschl’s gyrus has previously been linked to dyslexia, which involves severe reading difficulties. Research shows that this variation in cortical thickness does not draw a simple dividing line between people with or without dyslexia. Instead, it covers the general population, in which a thicker auditory cortex correlates with more skillful reading.
Does size matter?
Is thicker always better? As far as cortical structure is concerned, no, not necessarily. We know that the auditory cortex has more myelin in most people’s left hemisphere. Myelin is a fatty substance that acts as insulation for nerve fibers. It increases the speed of neural communication and can also isolate columns of brain cells from each other. Neuronal columns are thought to function as small processing units.
Its greater isolation and rapid communication in the left hemisphere are also thought to allow for the rapid, categorical processing necessary for language. We need to know whether a speaker uses the d or t category when saying darling or torn, rather than detecting the exact point at which the vocal folds begin to vibrate.
According to the “balloon model” of cortical growth, the greater amount of myelin compresses the cortical areas of the left hemisphere, making them flatter but more extensive. Thus, although the left auditory cortex may be thicker in good readers, it remains thinner (but much more extensive) than the corresponding right cortex.
This hypothesis was corroborated by the new study. The left hemisphere generally has larger cortical areas, but thinner and with a greater degree of myelin.
So, is it possible that the thinner it is, the better? Once again, the answer is no (necessarily).
Complex capabilities that require integration of information tend to benefit from a thicker cortex. The anterior temporal lobe, with its complex way of integrating information, is in fact the thickest structure of all cortical areas. An underlying mechanism may be the existence of more overlapping and interacting neurons, which process information more holistically.
Phonology is a highly complex skill, in which different sound and motor characteristics are integrated into speech sounds. It appears to be correlated with a thicker cortex in an area close to the left Heschl’s gyrus.
Although it is unclear to what extent phonology is processed in the Heschl gyrus, the fact that phoneticizers often have multiple left Heschl gyri suggests that it is linked to speech sounds.
