Brain Changes Seen in Preschoolers with ADHD

Attention-deficit/hyperactivity disorder (ADHD) is believed to begin just before a child turns 7 years of age. Neuroimaging studies have been carried out on children aged 7 and above; however, it is essential that we learn more about developmental deficits in different parts of the brain before age 7. In this study, 13 preschoolers (4- and 5-year olds) with language disorders similar to those seen in children with ADHD were compared to 13 control preschoolers. Imaging studies revealed that a region deep in the brain called the basal ganglia was smaller in children with ADHD symptoms than in those without such symptoms.

By the age of 4 years or so, behavioral symptoms causing concerns of ADHD become apparent. The behavioral problems that accompany ADHD make it hard for children to adjust to their environment. Preschoolers with ADHD are more accident prone and have higher chances of academic failure. Efforts are made to identify the disorder at an earlier stage to avoid adverse effects on a child’s development. Different areas of the brain are functionally linked. An injury to one part of the brain can affect the development of other parts of the brain. This study uses neuroimaging to find correlations between defects in certain brain areas at school age (7 years) and defects in other areas at an earlier developmental stage.

* Selected participants aged 4 to 6 years underwent brain magnetic resonance imaging (MRI). Cognitive functions such as memory, motor skills and attention were assessed. Parents of the participants answered a questionnaire about behavior-rating scales.
* A standardized computerized diagnostic instrument assessed psychiatric disorders and identified ADHD symptoms. Based on these assessments and parental reports, 13 preschoolers were included in the ADHD group and 13 in the control group.
* Differences in brain area volume and thickness were analyzed to determine the presence of a relationship between brain development and behavior.

* Age, intelligence quotient (IQ), male-female distribution, handedness and race were equivalent in the ADHD and control groups. Cerebral volumes of the two groups were not significantly different.
* The volume, surface area and thickness of the cerebral cortex,  as well as the volume of gray and white matter, were similar in the two groups.
* The volume of the right caudate, an area critical for learning and memory, was markedly reduced in the ADHD group.
* ADHD symptom severity was determined on the basis of standardized parental ratings. Left and right caudate volumes correlated with hyperactive symptoms in the ADHD group, but not with the inattentive symptoms.

Shortcomings/Next steps
The strict criteria used to include children with ADHD symptom made the results hard to generalize. This may also be the reason for similarities in IQs in the two groups. The sample size was too small to correctly gauge the effect of smaller differences in volume of other brain regions.

The study shows that at an earlier age, reduced volume of certain brain areas (left and right caudate nuclei) can be correlated to hyperactivity/impulsiveness symptoms, though not inattentiveness, in children with ADHD. Cortical volumes that are known to differ in children older than seven years are not significantly different in ADHD and normal children at earlier ages. Studies of animal models also suggest the involvement of caudate regions in the progression of ADHD. The reduced volume normalizes by puberty, an observation consistent with the reduction of ADHD symptoms around the same age. MRI studies at an earlier age, although harder to conduct, are useful in diagnosing ADHD.

For More Information:
A Preliminary Neuroimaging Study of Preschool Children with ADHD
The Clinical Neuropsychologist, June 2011
By E. Mahone, PhD; D. Crocetti, et al., The Kennedy Krieger Institute, Baltimore, MD; Johns Hopkins University School of Medicine, Baltimore, MD

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