A consensus of opinion exists among the scientific community that ADHD (attention deficit hyperactivity disorder) is a biological condition resulting from varying, yet scientifically undefined, neurological dysfunctions. Traditionally, the majority of research results suggest that a region of the brain known as the pre-frontal cortex, situated behind the forehead, controls many of the behaviors and traits associated with ADHD, given that the anterior part of the brain is associated with executive functions: problem solving, attention, reasoning, planning, and decision making – cognitive functions noticeably impaired in those with ADHD. However, gradually, with the aid of neuroimaging techniques, neurologists and neuroscientists have been able to map additional neural mechanisms responsible for ADHD symptoms more accurately.
Basal Ganglia – MRI Magnetic Resonance Imaging Studies
Various MRI (Magnetic Resonance Imaging) studies over the last two decades, show significant volume and structural differences between ADHD and non-ADHD children in areas of the basal ganglia – a group of sub-cortical nuclei receiving input from the entire cerebral cortex but primarily from the frontal lobes, parts of which regulate movement and cognitive functioning. However, according to Anqi Qiu, Ph.D et al, The American Journal of Psychiatry, 2009, typical research using MRI studies of three basal ganglia components – the caudate, putamen, and globus pallidus – presents inconsistent volumetric measurement results.
Past Basal Ganglia Studies
Aylward et al, 1996, reported that children with a co-diagnosis of Tourette syndrome and ADHD showed differences in volume of a major component of the basal ganglia – the left globus pallidus – reputed to regulate attention. Imaging confirmed the left globus pallidus to be significantly smaller in comparison to children with only Tourette syndrome or normal control children.
Aylward made follow-up studies, MRI scans were performed, and measurements were taken of areas of the basal ganglia: the caudate, putamen and globus pallidus. The researchers discovered differences in the volume of the globus pallidus between the control group and the ADHD group, and ADHD and Tourette syndrome group, and concluded that left hemispheric basal ganglia anomalies are associated with ADHD.
Besides the research undertaken by Aylward, Anqi Qiu, et al (2008) note that further studies found decreased right caudate volumes, and reversed caudate asymmetry, i.e., not the typical right-left caudate relationship. In addition, the studies noted a decreased volume of the putamen, reversed putamen asymmetry, and decreased volume of the right globus pallidus.
This study concludes that these varying differences and inconsistencies may be attributable to the biological heterogeneity associated with ADHD, including sex-specific effects or inconsistencies caused by limitations in anatomic imaging methods together with focusing research only on volumetric abnormalities.
LDDMM – Advanced Computational Anatomical Imaging
In order to shed light on research inconsistencies, and to improve on previous studies limited to volume analysis and comparison, the Center for Imaging Science at Johns Hopkins University and Kennedy Krieger researchers Anqi Qiu, Ph.D et al (2008) collaborated in this study. The team of researchers used large deformation diffeomorphic metric mapping (LDDMM) to examine the effects of ADHD, gender, and their interaction on basal ganglia shapes.
LDDMM, a computational instrument, provides volumatic information and detailed analysis of the morphological shape of cortical and subcortical brain regions, thus allowing for a more accurate analysis of brain structures than that provided by MRI studies
Using a control group of 66 typically developing children (35 boys, 31 girls) and 47 children with ADHD (27 boys and 20 girls) this particular research revealed that when compared with boys in the control group, the boys with ADHD had the following differences:
- Significantly smaller basal ganglia volumes were observed between the two samples.
- Prominent differences in basal ganglia shapes existed in the two groups.
- Outward and inward surface deformation created ‘multifocal shape differences’ of the basal ganglia of the ADHD sample.
On the contrary, no differences were found in the girls with ADHD. This suggests that gender differences affect neuropathophysiologic processes and neuroanatomic formations.
Recent Research Reveals Reduced Basal Ganglia Volumes
A more recent, ongoing longitudinal study by the Kennedy Krieger Institute, published June, 2011, also reports of significantly reduced caudate nucleus volumes in 13 pre-schoolers presenting with ADHD symptoms.
The differences were found after the researchers examined high resolution MRI brain images of 26 preschoolers (ages 4 and 5) both with and without symptoms of ADHD. The size variations of the caudate nucleus of the children with ADHD symptoms correlated with the parents’ reports of hyperactivity and impulsivity. The findings led the researchers to conclude that volume differences in the basal ganglia, particularly the caudate nucleus, may be a factor causing ADHD symptoms in children.
Accurate Neuroimaging Tools Lead to Solutions
A survey of research over the last decades undoubtedly reveals that ADHD is a neurologically based behavioral disorder. Neuroimaging studies such as MRI, functional imaging techniques: fMRI and SPECT, and now the more powerful and precise LDDMM, can identify and isolate the specific core neuroanatomic areas controlling the behaviors that define ADHD. In addition, the research using LDDMM accentuates the importance of conducting accurate imaging studies using more than one measure of comparison.
Research discovering unique variations in brain volumes and structures that may play key roles in the presenting behaviours of ADHD further emphasizes the existence of this disorder and may initiate further research into investigating ways that may alleviate the personal and environmental affects of ADHD.
- Aylward, E., Reiss, A., et al. Basal Ganglia Volumes in Children with Attention- Deficit Hyperactivity Disorder. Journal of Child Neurology (1996). 11:112-115.
- Anqi Qiu, Ph.D., Deana Crocetti, B.S., Marcy Adler, B.A., E. Mark Mahone, Ph.D., Martha B. Denckla, M.D., Michael I. Miller, Ph.D., and Stewart H. Mostofsky, M.D. Basal Ganglia Volume and Shape in Children With Attention Deficit Hyperactivity Disorder. American Journal of Psychiatry. (2009). 166(1): 74–82. Accessed November 27, 2011.
- Center for Imaging Science. Biomedical Informatics Research Network. LDDMM Volume. Accessed November 21, 2011.
- Kennedy Krieger Institute. Brain Imaging Study of Preschoolers with ADHD Detects Brain Differences Linked to Symptoms. (2011). Accessed November 27, 2011.
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