Sensitivity and Specialization in the Occipitatemporal Region: Differences in Dyslexic Children

Wednesday, August 4, 2010

Accessibility: Advanced/intermediate

Early research on the role of the occipitotemporal region in reading often focused on characterizing a single region in the mid fusiform, commonly called the visual word form area. Since then, focus has gradually shifted from a single region to the entire length of the occipitotemporal region, looking at how the sensitivity and tuning changes as you move from posterior to anterior regions.



Van der mark used an approach like this to look at dyslexic and control children aged 9-12 years. Eighteen normal reading and twenty four dyslexic children performed a phonological lexical decision task in the scanner. Children saw words, pseudohomophones (words that sounded like real words but spelled differently, like “taksi”), pseudowords (pronounceable nonwords), and false fonts. The children were asked to decide whether something sounded like a real word. For example, the correct response would be “yes” for words and pseudohomophones and “no” for pseudowords and false fonts.

The children with dyslexia did worse for pseudohomophones and pseudowords and performed similarly to the controls for words and false fonts.

The authors report two main findings. First, the control children showed a gradient of print specialization in the occipitotemporal region, with more activation to false fonts in posterior regions and more activation to real letters and anterior regions. The control children did not show this trend.

Second, control showed more activation for pseudowords and pseudohomophones than words, while children with dyslexia didn't.

This is a nice study that takes a more nuanced approach to dyslexia brain differences. Brem and colleagues also got similar results with the words and false fonts.

By now there's quite a bit of literature on the specialization of the visual word form area. My own struggle, as I’m also doing this type of research, is the question of what does it all mean? We have all the studies now showing brain differences between control and dyslexic children, but what does it mean to have more or less activation? That the brains of dyslexic children process words differently? I could've told you that before we stared.

So what would help? Perhaps the next step in dyslexia research, now that we've mapped out the basic differences, is to zoom in as much as we can on the relationships between brain differences and behavioral differences. Perhaps more fine grained behavioral measures would help, or more interventional studies that looked at brain activation before and after training. It may also help to look at functional connectivity and how different brain regions interact. Anyone else have ideas?



van der Mark S, Bucher K, Maurer U, Schulz E, Brem S, Buckelmüller J, Kronbichler M, Loenneker T, Klaver P, Martin E, & Brandeis D (2009). Children with dyslexia lack multiple specializations along the visual word-form (VWF) system. NeuroImage, 47 (4), 1940-9 PMID: 19446640

5 comments:

jjdebenedictis August 4, 2010 at 12:06 PM  

As a layperson, I would think the most useful thing to explore is how the differences get in the way of a dyslexic's ability to read and write, i.e. what's actually happening in the brain when they make a mistake? That could lead to more effective therapies for training the brain to do the right thing.

Livia August 4, 2010 at 12:13 PM  

Yes, we'd like to get there too. It's surprisingly hard to narrow in on what a brain difference means, because all we have to go by is more or less signal in Blob x.

Cat Woods August 4, 2010 at 1:17 PM  

Livia,

I love following your blog. As a mom of a severely dyslexic child, I am very interested in the connection between dyslexia and over all behavior function-not just in terms of reading and writing.

I always tease my son that God hardwired him differently than the rest of us, something that has become evident based on research. What is lacking, though, is how this rewiring affects all aspects of their growth and development.

During his testing, I had the luxury (and pain) of watching him answer the questions that determined his strengths and weaknesses regarding the written word. It amazed me how much his dyslexia affects his entire thought process and view of the world. It also explains why he does some of the otherwise inexplicable things he does.

Interesting work. Keep it up!

Ken Arnold August 4, 2010 at 8:50 PM  

I wonder if this means that dyslexics have some trouble suppressing meaningless information, i.e., that if some processing fails to yield a plausible result, normally the implausible results are suppressed, but in dyslexics they are allowed to pass on to further processing? That would explain the activation of higher-level processing for pseudowords, and maybe also some of the confusion that dyslexics experience.

Livia August 5, 2010 at 4:59 AM  

Ken -- Brilliant. And there's some literature that speaks to that, although not directly. Hmm....

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