Researchers at the Kennedy Krieger Institute have found differences in the brain development of preschool children presenting with early symptoms of ADHD. Dr. Mark Mahone is the Director of Neuropsychology at the Kennedy Krieger Institute and lead author of the study.
Since preschool children with symptoms of ADHD are at significant risk for social and academic difficulties compared to typically developing children, Dr. Mahone and his team seek to better understand the neurobiological development of ADHD. Knowing more about brain growth patterns in young children with ADHD has a great deal of potential for not only helping to increase early identification of ADHD, but also in the development of specific and targeted treatments that may minimize the harmful impact of symptoms as the child ages.
Q: Can you explain a little about neuroimaging and how it is used to understand brain development or differences associated with ADHD?
Dr. Mahone: There are several types of neuroimaging (or brain imaging) which are essentially used to take pictures of the brain, in order to map out its structure and function in a relatively non-invasive way. This is usually done with a magnetic resonance imaging (MRI) scanner. The MRI scans for research studies are usually more detailed and take longer than those used for routine clinical procedures.
Some neuroimaging is used to estimate actual brain volumes in different parts of the brain. This type is called volumetric MRI or anatomic MRI. By looking at brain volumes in groups of individuals, researchers can determine whether individuals with a particular disorder (e.g., ADHD) have different brain volumes (larger or smaller) than individuals without the disorder. We can look specifically at different regions of interest (ROIs) in the brain to see whether some are more “different” than others. In children, we can also look to see how the size of each of these regions changes over time, and whether the pattern of change is different in children with (for example) ADHD, compared to children without ADHD. In addition, once brain volumes in different regions are measured, researchers can see how reduction (or increase) in these volumes is associated with certain behaviors or cognitive skills.
Other types of neuroimaging often used in children (but not used in the present study) include:
- Functional MRI (fMRI), which examines blood flow in the brain associated with performing different tasks
- Diffusion tensor imaging (DTI), which looks at patterns of water dispersion throughout the brain to estimate the integrity of white matter connections in the brain
- Magnetic resonance spectroscopy (MRS), which uses MRI to look at chemical metabolites in different regions of the brain.
Q: What did your research find in regards to brain differences in preschool children presenting with early symptoms of ADHD?
Dr. Mahone: In our study, we determined that a small region deep in the brain called the caudate nucleus was significantly smaller in preschool children with symptoms of ADHD than it was in a group of age- and sex-matched children without symptoms of ADHD. In addition, we also found that, among the children with ADHD, the size of the caudate nucleus significantly predicted the severity of ADHD symptoms; but not in children without ADHD. The caudate nucleus is a structure that is involved in the development of attention and cognitive control, as well as the development of motor control. In contrast, the cerebral cortex, which researchers believe develops later in children, was not abnormal.
Q: Why is it important to understand early brain growth patterns underlying the development of ADHD?
Dr. Mahone: By the time children with ADHD reach school-age, the research shows that there are multiple areas of the brain that are smaller and less developed than in children without ADHD. These areas include the cerebral cortex (which is thought to be responsible for higher level cognitive skills), as well as subcortical areas, such as the basal ganglia (including the caudate nucleus), and the cerebellum. In the brain, these subcortical areas have strong connections with the cerebral cortex. Researchers think that during early development in children, the early development of the subcortical brain regions influences the later development of the cerebral cortex. In other words, if the subcortical parts of the brain develop atypically early on in life, it will affect the development of the cerebral cortex, which controls higher intelligence and learning.
Thus, we are seeking to identify exactly how and where the brain develops atypically early on among children who present (as toddlers and preschoolers) with symptoms of ADHD, and how this atypical brain development is associated with onset of (and severity of) these symptoms. If we know which areas of the brain become abnormal earliest in ADHD, it will help us develop more specific and targeted treatments designed to intervene earlier, in order to help “normalize” development of the brain and behavior earlier in life, with the expectation of better outcomes.
Interview with Dr. Mark Mahone continued on page 2.