Increasing White Matter


The brain consists of approximately 50% of grey matter and 50% of white matter. If you think of the brain as a computer, the grey matter (nerve cells) of our brain is the computer and the white matter is the cables that connect everything together and transmit signals.

Recent studies have identified features of the white matter that predict reading outcomes in dyslexia and reading-related skills. (e.g., phonological awareness). It has also been found that there are rapid, measurable changes in white matter following short-term training.

Participants

In their study, Huber et al. (2018) recruited 24 children aged between 7 to 12 years who either had a clinical diagnosis of dyslexia or whose parents reported they had reading difficulties.  An additional 19 participants were recruited, as a control group, who were matched for age but not reading level. Of this control group, 10 were assessed as having typical reading skills and 9 were assessed as having reading difficulties.

Research Design

The children with reading difficulties in the intervention group were enrolled in an 8 week one-on-one training program which focused on explicitly teaching phonological and orthographical skills for 4 hours a day, 5 days a week. Participants in the control group continued attending school as per normal.

Participants in the intervention group had an MRI scan before the intervention began, after 2.5 weeks of intervention, after 5 weeks of intervention and at the end of the intervention. Participants in the control group also had MRI scans at the same time.

Results

Prior to the intervention MRI scans showed a correlation between white matter tracts and reading skills. It was also found that none of the white matter tracts that were significantly correlated with reading skills were correlated with maths skills or general academic ability.

Participants in the intervention groups showed a significant improvement in their reading skills during the 8 week intervention, but there was no evidence of changes in maths skills over this time, confirming that the intervention only impacted on reading skills. Furthermore, this growth in reading skills was specific to the intervention group and not reflected in the control group.

Examination of the white matter tracts associated with reading skills showed measurable changes in the intervention group but not in the control group. In particular, there was an increase in white matter in tracts connected to the reading neural circulatory and generally considered to support separate aspects of reading, specifically:

  • Left AF (arcuate fasciculus) tracts which have previously been linked to phonological awareness
  • Left ILF (inferior longitudinal fasciculus) which is especially involved in word recognition

However, the effects of the intervention were not limited to those regions. The researchers suggest that this was either because reading depends on the coordination of a large cortical network OR it may be that this type of widespread effect may occur during any intensive educational experience.

Discussion

  • Although there were significant changes in white matter generally, these effects did not result in ‘normalisation’ of the tracts as would be observed in a typically developing reader.
  • This would suggest that remediation is accomplished through compensatory mechanisms that differ from those supporting the acquisition of skilled reading in typically developing readers.
  • The posterior callosal connection (which connects the left and right hemispheres) was remarkably stable. In fact, the structure of the posterior callosal connections (CC) differs in both children and adults with dyslexia compared to typically developing readers.
  • However, the posterior CC are known to mature relatively early. Consequently, the researchers suggested that the participants in this study may have already been outside the ‘sensitive period’ in which experience might shape these connections (i.e., training at a younger age may have resulted in changes to the posterior CC).
  • It is also worth noting that the recorded correlations between anatomy, behaviour and experience changed from week to week. Therefore, correlations measured at any single time point may result in an incomplete and potentially misleading view of these relationships.

Further Thoughts

  • Explicit, intense, direct instructions in reading programs focused on teaching phonological and orthographic skills make measurable differences to both reading and brain structures.
  • It is likely that the earlier such interventions are put in place the better the outcomes and the higher the likelihood that the resulting brain structures will reflect typically developing readers.

Reference

Huber, E., Donnelly, P., Rokem, A., & Yeatman, J. (2018). Rapid and widespread white matter plasticity during an intensive reading intervention. Nature Communications, 9, Doi: https://doi.org/10.1038/s41467-018-04627-5

 

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