Wednesday, February 25, 2009

Connections: White Matter and Learning

I became interested in the topic of literacy in children while working with a class of 5-6 year olds at the Early Childhood Center on Sarah Lawrence Campus. From the teaching standpoint, this is the age in which the foundations for literacy are laid. There is also evidence that this time is a critical period in brain development. At the ECC, teachers take a “developmental” approach to learning, believing that with encouragement and support children will learn to read at their own pace and in a natural way. Unfortunately, in our society much emphasis is placed on the speed rather than the quality of skills children acquire. As a result, many children who develop more slowly than others are quickly diagnosed with dyslexia or other disorders. How can our knowledge of the brain aid us in our understanding of how children attain literacy? Are there direct correlations between differences in the brain and level of ability? How can our growing knowledge of the structure of the brain influence the way we teach and diagnose children learning to read?
Below I hope to give a brief overview of a study headed by Brian Wandell, chair of the psychology department at Stanford University, which addresses some of these questions.

Previous studies have used brain imaging to establish the connection between the left temporo-parietal cortex and reading ability in adults. Wandell set out to find if this connection applied to children at an age where reading skills are growing rapidly. He and his team hypothesized that similar findings in the structure of white matter in the left temporo-parietal lobe of children would indicate that these neural pathways play integral role in how we develop fluent reading. An alternate hypothesis maintained that if the finding were found to be different between children and adults of varied ability, it could suggest that many years of differential reading experiences could be the cause of structural disparity in adults.

Simply: Does structure define ability? Or Does ability define structure?

Diffusion Tensor Imaging (DTI)
DTI, a form of magnetic resonance imaging, is a significant component of Wandell’s study. While an MRI can give us a good anatomical image in which we can differentiate gray and white matter in the brain, DTI allows researchers to look at the fine tissue structure of white matter. Technically speaking, this nueroimaging method measures the diffusion of water molecules in brain tissue. In simpler terms, DTI allows us to identify and examine different regions of white matter. The direction of the water diffusion gives us insight into the alignment of white matter axons in areas of the brain. Essentially, what we are looking for are the pathways in the brain areas already defined as being responsive during reading and phonological tasks in adults. We assume these pathways also exist in children, what we want to find is if they differ among children of varied reading abilities.

Areas of dense white matter were studied to obtain information about the direction of diffusion, indicating the fiber tracts of white matter demonstrating significant pathways. Fractional Anisotropy (FA) is a measure of direction within a given area or voxel. A high FA value within a voxel would indicate highly directional diffusion. Coherence Index (CI) is used to measure the overall direction of multiple adjacent voxels. High CI would reflect the agreement of fiber direction in neighboring voxels, demonstrating the existence of strong neural pathways.

For their study, the researchers chose 14 children between the ages of 7 and 13, who were by all accounts healthy and normal. These children were classified as either “normal” or “poor” readers based on a series verbal and performance related tests. Among the groups there were no significant differences in ages, genders, parental education of socioeconomic status. Subjects classified as “poor” readers had composite scores that placed them below the 30th percentile in reading. The children in this group had all been previously diagnosed with dyslexia by a psychologist, although it is interesting to note that they also presented varying degrees of deficits in all areas.
Each child received four 3 minute brain scans that were then averaged. Scans specifically focused on voxels in the temporo-parietal region. All reported differences between the two groups were limited to the white matter regions common to all brains.

Comparing data from both groups, researchers were able to conclude that there were significant differences in FA and CI in voxels in the temporo-parietal region of the brain. These differences indicate that there is a connection between the structure of white matter and a specific cognitive ability among healthy children. This further suggests, although it does not prove, that the difference may be the cause of poor reading development rather than the consequence.

In the end
So structure does in a way indicate ability. Where does that leave us? Wandell and his team may have found a discrepancy in the brains of “normal” and “poor” readers, but there are obviously many other factors involved that fall beyond the scope of this study. The researchers concluded that FA value could be more useful in predicting average or above reading scores rather than in diagnosis of reading disabilities.

0-2 years –rapid growth in axon diameter and myelin strength

3-6 years –significant change in the frontal networks

7-11 years- peak growth rates in fibers connecting sensory-reading cortex

In the years prior to puberty, the section of the corpus callosum which connects cortical region located in and around significant language processing areas can increase as much as 80%.

It is not known specifically how the brain continues to grow during adolescence and through adulthood, although there is indication that growth takes place.

It is clear that there is a relationship between the functional and anatomical development of our brain and the acquisition of skills such as reading.

A teacher at the Early Childhood Center told me recently that teaching a child to read is like teaching a baby to walk. You can hold an infant on its feet, show them how to move their legs, but you can’t force it. One day, it just clicks, and it is no coincidence that walking will occur at a point when the body has developed the muscles and abilities it needs to support itself.
The figures above indicate that we are moving toward a better understanding of how the brain grows and changes as we age. It strongly suggests a connection between this growth and the acquisition of knowledge. However, it does not tell us how each individual’s brain develops or show with authority how we can define differences in the way children learn. Certainly for every statistic we create there will be an exception.
If stages of brain development equip children with the various tools needed to attain literacy, then we can no sooner impose reading on a two year old than we can induce their brain to grow. How
then can we say that a child must conform to a specific timeline in their learning, how can we presume that if they do not perform up to a set standard within a restricted learning style that they are mentally deficient. There are undoubtedly children who do have disabilities related to learning, but we can’t afford to generalize when to do so would be to upset such an important foundation.

I can only conclude that children will learn in their own time and all we can do support them and surround them as many paths as possible on the road to knowledge. Hopefully, with time, there will be a point where “it just clicks.”

Bernard, Sara. “Wired for Reading: Brain Research May Point to Changes in Literacy Development.”

“Children’s Reading Performance is Correlated with Whit Matter Structure Measure by Diffusion Tensor
Imaging.” Deutsh, Gayle K., Robert F. Dougherty, Roland Bammer, Wai Ting Siok, John D.E. Gabrieli, and Brian Wandell. 2003. Department of Psychology, Department of Radiology, Stanford University, Stanford, CA

Ben-Schachar, Michal, Robert F. Dougherty, and Brian A. Wandell. “White Matter Pathways in Reading.”
Current Opinion in Neurobiology 2007, 17: 258-270. ScienceDirect.

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