Dyslexia Brain Differences Show Up Before Formal Reading Instruction

Thursday, January 28, 2010

Last time, we talked about early behavioral differences between prereading children that predicted future reading impairment. Today, we’re continuing on the theme of early predictive differences, this time in the brain.

The question of how early brain differences arise is a worthwhile one. We want to know whether the dyslexic brain is tackling reading differently from the very beginning or if these brain differences arise after some reading experience, perhaps reflecting compensatory strategies that the children may have developed.

Specht and colleagues (Scandinavian Journal of Psychology 2008) conducted a brain imaging study on Norwegian children (a good population to study because reading instruction starts in second grade in Norway). The basic goal of their experiment was to scan 6 year olds (before they learned to read) and see if they process words differently depending on their risk for dyslexia. Unlike the Lervag study, this study was not longitudinal. Specht and colleagues determined which kids were at risk for dyslexia using a risk index that took into account factors like heredity, language development, and other factors.

Kids looked at four kinds of stimuli during an fmri scan: pictures, logos, regular words and irregular words while performing a categorization task (“Is this something you can play with?” and similar questions). I won’t spend too much time comparing between conditions because I’m not clear on what characteristics were controlled for between the stimulus types.

There were differences between the at-risk and normal reading group in all conditions. There were several interesting findings. First, risk index score correlated with increased activation when looking at words in the angular gyrus, an area that has been reported to be involved in language/phonological processing.

Our old friend, the visual word form area, also shows up. At a more liberal statistical threshold ( p<.001 uncorrected and with a small volume correction) they found that risk index score correlates negatively with left occipitotemporal activation when viewing irregular words.

So what does this mean? For one thing, differences arise early, before formal reading instruction. The two groups did not differ significantly on standardized reading measures at the time of testing (although there was a trend (p<.096) towards a difference in reading scores. So there seems to be something different about how these kids approach words from the very beginning. It would be interesting to know what is driving these differences. I wonder what strategies the kids were using to in the scanner to complete the categorization task, especially since they couldn’t read yet. For word conditions, kids only had an accuracy of 20-30%. What were they doing for the words they couldn’t read? Were the scanner differences driven by the words they could recognize, or all the words?

I’m particularly puzzled by the VWFA findings. The VWFA is usually thought to develop based on expertise with letters Does this mean that even before reading instruction there is some difference in expertise between kids at risk and not at risk? Interesting questions for future investigation.

Specht K, Hugdahl K, Ofte S, Nygård M, Bjørnerud A, Plante E, & Helland T (2009). Brain activation on pre-reading tasks reveals at-risk status for dyslexia in 6-year-old children. Scandinavian journal of psychology, 50 (1), 79-91 PMID: 18826418


debyee January 28, 2010 at 11:21 PM  

hrm, there are numerous articles arguing that dyslexia is a 'brain issue' and is something that is in the circuitry of the brain, independent on the learning environment (nature over nurture). More curiously, what do the risk indexes reveal/imply about the children being tested? Does it mean that these children are less or more likely to have dyslexia? Is there only negative correlation with only irregular (and i suppose that implies foreign?) words? Do you have any speculation on what these differences that these young children may be experiencing concerning how they read words before they are taught to read?

Livia Blackburne January 29, 2010 at 8:12 AM  

Deb -- It's never just nature or nuture -- it's almost always an interaction. Your genes put you at risk, but better education may help you compensate. The risk indexes calculate the chance that they will have dyslexia. Irregular words refer to words that aren't spelled according to rules, not foreight words. I'm not quite sure what you mean by the last question -- perhaps the children arealready learning about words despite lack of formal instruction, and the dyslexic children are showing a disadvantage.

Jason January 30, 2010 at 12:16 PM  

I'm also puzzled by the OT finding, because it does put the skill-zone interpretation into question. But presumably if the kids are able to read the words they shown in the scanner with some accuracy (did they report accuracy and reaction time?) then even if they haven't had direct reading instruction, they've had some incidental reading instruction, and they've certainly had some exposure to print.

Jason January 30, 2010 at 12:25 PM  

Also, totally adding you to my google reader :-)

Victoria February 8, 2010 at 12:51 AM  

Came via your creative writing blog and I'm very glad I did!! As a speech path I don't believe we understand the complex neurology involved when it comes to reading disorders so I'm loving the information!!

I am curious, however, old research (late 90's) was suggesting the individuals with dyslexia have an over-reliance on the left-frontal areas (particularly Broca's area)thus resulting in slow manual, letter by letter reading - is this still relevant or has much current research indicated otherwise?

Murfomurf February 23, 2010 at 4:31 PM  

I'm going to look up the studies shortly to see what I make of them- I'm not clear whether it means there are structural (connections? white/grey matter?) differences, functional differences or developmental stage differences between ordinary kids and "dyslexic" ones. Also, how does dyslexia manifest itself in children learning to read in languages with different sound/picture symbols, like Chinese, Japanese and Cyrillic? I think inter-language comparisons would have to be included to get a complete idea of what the deficit is. Has anyone looked at the in-built cue properties of language symbols for children at various ages/stages? ie. Do some shapes have more salience (natural meaning) before the language ascribes specific meanings to specific shapes? eg. Do symbols containing circles (eg. "o", "b", "p" have more or less natural appeal (or cue value)- to be looked at first or for longer, in an array? Don't mind me- I'm an old ex-researcher in autism and haven't been keeping up with the literature!

Livia Blackburne February 25, 2010 at 10:46 AM  

Murfomurf -- there's some cross cultural research on dyslexia. check out Wai Ting Siok's work

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