On the Road to Reading: Commuting Through the Complex Connectome
Image adapted from here
Caught in traffic during your morning commute? Stuck in stop-and-go on the highway? Tired of trying to navigate ongoing construction downtown? Believe it or not, this frustrating experience might be a close example of what a reading disorder looks like.
A recent study published in 2021 from Western University has found that information ‘traffic’ in the brain may be partially responsible for poor reading skills. Just like the roads that connect a city, the brain relies on a network of interconnecting pathways to send information from one area to the other. It’s the efficiency of this network – called a connectome – that might just make the difference between strong and struggling readers.
The brain can be divided into two types of material: grey matter and white matter. Grey matter refers to the pink tissue on the surface of the brain which sends and receives information. White matter, on the other hand, connects your grey matter regions together and allows the brain to communicate with itself. Most mental activities we do – reading, daydreaming, even seeing and hearing – requires coordination of multiple parts of the brain. However, these brain regions are not always nearby one another, making communication essential. If we consider the brain as a collection of cities, grey matter would make up the neighbourhoods and destinations while white matter acts as the roads that connect them.
In any city there are different types of roads that serve different purposes for the population. Small residential roads connect neighbourhoods and conduct local traffic; large main roads help direct cars through the city with the use of traffic lights, interchanges, and other controls; and highways move large volumes of traffic between cities. Your brain’s connectome has a pretty similar structure, with three types of white matter connections. Local pathways connect nearby brain regions into neighbourhoods. Feeder pathways connect these neighbourhoods to hubs – the brain’s version of an interchange. Finally, a collection of pathways called the rich-club network act as the ‘highways’ by moving information across the brain with hub-to-hub connections.
(The connectome: Think of it like the Greater Toronto Area; there are several cities which connect to Toronto, and thousands of commuters trying to move between them daily. Picture from article: Lou et al., 2021)
It takes a skilled city planner to make sure traffic flows efficiently through town. Our brains take on the task of laying down many of these roads during childhood, which is often when reading disorders (such as dyslexia) are noticed. Reading disorders change the organization and communication of a collection of brain regions called the reading-network.
To better understand how reading disorders affect the reading-network, PhD student Chenglin Lou designed a study to compare differences in the connectomes of good and poor readers. The study recruited 64 English-speaking students who were between the ages of 8 and 15. Of these participants, 18 students had a diagnosed reading disorder, while the rest ranged from poor to strong readers. Lou and colleagues used two types of neuroimaging in their study: fMRI (functional magnetic resonance imaging), which images grey matter, and DTI (diffusion tensor imaging), which images white matter.
After neuroimaging, both image types were combined to create connectome maps for each participant. Connectome maps gave a picture of the brain’s reading-network, and identified the hubs and white matter pathways that connected the network. These maps organized the connectome into: local areas connected by the smallest local pathways; hubs connected to local areas by feeder pathways; and the rich-club network, which connect areas across the reading-network and beyond. Thanks to the combination of neuroimaging methods, connectome maps also supplied information on the strength and efficiency of those connections, much like how Google Maps can give updates on traffic conditions. By comparing connectome maps to the reading skills of their participants, the researchers began to find differences in the way strong and poor readers managed ‘traffic’ across the reading-network.
When it came to communicating across the brain, it was the feeder pathways that made the difference. Stronger readers had more feeder pathways connecting local areas to hubs than poor readers. They also had stronger, more efficient feeder pathways than poor readers. Going back to our city analogy, this is akin to having more main roads in a city, capable of handling more traffic and providing easier access to the highway. As any commuter knows, well organized access in and out of the city makes for a faster, less cumbersome travelling experience. For strong readers more feeder pathways mean more ‘roads’ can be taken to travel from local regions to the rich-club network. Additionally, stronger feeder pathways better organize information going to and from the rich-club network. Both traits make for faster connectome communication and easier reading.
Poor readers, on the other hand, had fewer and less efficient feeder pathways than strong readers, making communication more difficult across the entire reading-network. Since feeder pathways connect with local regions and the rich-club network, they can slow the speed of communication locally and across distant regions of the brain. Consider, for example, how construction on a main road can have a domino-like effect on traffic conditions across the city. This sounds pretty dire for students struggling to read. However, Lou’s study notes that even though communication was disrupted in the brain, connection strength between local pathways and within the rich-club network was not. In essence, if we can improve the traffic conditions on feeder pathways, then local roads should clear up too.
The idea of improving traffic in white matter ‘roads’ may seem limited to the level of the brain, but this research may also offer some new ideas for reading instruction in schools as well. Plenty of additional research has gone into identifying what makes an effective school reading program. Programs that teach students how to use multiple strategies are among the most effective for improving reading comprehension in struggling readers. Reading comprehension strategies help students make connections to their readings, and engages critical-thinking methods. By teaching students how to use many different reading comprehension strategies, they can learn to pick and choose what works best for them.
With insight from Lou’s connectome study, we may start to see how these types of reading programs could change the brain over time. If communication across the reading-network is a problem, then teaching students how to use multiple reading strategies might also help build new, more efficient, ‘routes’ for information to travel. Since reading comprehension strategies focus on critical-thinking, these new routes may also use parts of the connectome that aren’t reading-specific, like the rich-club network. Essentially, effective reading programs may teach students to focus on building new ‘highways’ to get across the reading-network, rather than trying to reconstruct the same old overburdened roads.
More research needs to be done before we can fully understand how changes in reading strategies affect our brain’s connectome, but these studies are an encouraging step forward. Looking to the future, with enough research we may just see that traffic jams are a thing of the past! At least for the readers out there.
Main Article:
Lou, C., Cross, A. M., Peters, L., Ansari, D., & Joanisse, M. F. (2021). Rich-club structure contributes to individual variance of reading skills via feeder connections in children with reading disabilities. Developmental Cognitive Neuroscience, 49, 100957. https://doi.org/10.1016/j.dcn.2021.100957
Supporting Articles:
Filderman, M. J., Austin, C. R., Boucher, A. N., O’Donnell, K., & Swanson, E. A. (2022). A Meta-Analysis of the Effects of Reading Comprehension Interventions on the Reading Comprehension Outcomes of Struggling Readers in Third Through 12th Grades. Exceptional Children, 88(2), 163–184. https://doi.org/10.1177/00144029211050860
Jitendra, A. K., Burgess, C., & Gajria, M. (2011). Cognitive strategy instruction for improving expository text comprehension of students with learning disabilities: The quality of evidence. Exceptional Children, 77(2), 135–160.
Klingner, J. K., Vaughn, S., Arguelles, M. E., Tejero Hughes, M., & Ahwee Leftwich, S. (2004). Collaborative Strategic Reading: “Real-World” Lessons From Classroom Teachers. Remedial and Special Education, 25(5), 291–302. https://doi.org/10.1177/07419325040250050301