ADHD and Brain White Matter Deficits

Structural brain imaging studies in ADHD fail to find consistent differences from non-ADHD populations.

However, there is increasing evidence linking ADHD to changes in brain white matter function.

An example of these findings is a recent study from China examining white matter in children with ADHD.

ADHD is typically subgrouped into inattention (ADHD-I), hyperactivity ADHD-H or combined categories (ADHD-C). In the recent Chinese study, inattention and combined subgroups of children were compared to control children without ADHD.

Diffusion tensor imaging or DTI was utilized in this study. This imaging techniques allow study of white matter function in various brain regions. A variety of specific connectivy circuits have been identified. The brain white matter connects brain regions in circuits allowing coordinated processing, cognition and behavior.

Using DTI measures of white matter integrity and function are calculated. These parameters are known as fractional anisotropy, radial diffusivity and axial diffusivity. 

The key findings from the Chinese study included the following:

• ADHD-I children showed white matter abnormalities in the temporo-occipital circuits
• ADHD-C showed the temporo-occipital abnormalities found in ADHD-I but had additional white matter abnormalities in the frontal-subcortical and fronto-limbic circuit regions
• Deficits in the brain region known as the cuneus and precuneus correlated with inattention scores 

This study is one of the first to suggest distinct brain white matter regional abnormalities in two subtypes of ADHD. Although both subtypes showed abnormalities in the temporo-occipital circuits, ADHD-C alone showed abnormalities in circuits related to motor function.

These brain white matter differences in a group of children of mean age 9 years may represent developmental delays that improve over time. Many adolescents and adults with childhood ADHD symptoms show significant improvement in later stages of development. 

However, some adolescents and adults will have persistent ADHD symptoms. In the next post, I will summarize a brain imaging study of adults with ADHD.

Readers with more interest in this study can access the free full-text manuscript by clicking on the PMID link below.

Figure is a screen shot from the iPad app Brain Tutor. It shows the white matter circuit fibers connecting the temporal lobe and occipital lobe. Deficits in this circuitry were noted in both types of ADHD in the present study.

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Lei D, Ma J, Du X, Shen G, Jin X, & Gong Q (2014). Microstructural abnormalities in the combined and inattentive subtypes of attention deficit hyperactivity disorder: a diffusion tensor imaging study. Scientific reports, 4 PMID: 25363043