Attention-Deficit Hyperactivity Disorder, or ADHD, is a neurobehavioral disorder characterized by significant brain structure and function abnormalities. Due to the significant advances in neuro-imaging methods during the last decade, much more is currently known about these abnormalities.
Neuro-imaging
Brain imaging forges a remarkable link between medicine, psychology and neuroscience. It uses different techniques to visualize the structure, or function of the brain. Structural neuroimaging, such as Magnetic Resonance Imaging, or MRI, provides detailed 3D images of the structure of the brain. Functional neuroimaging, such as functional MRI, often aims at understanding the relationship between an increased or decreased activity in certain brain area and specific cognitive functions, such as memory or learning.
Magnetic Resonance Imaging
Magnetic Resonance Imaging, or MRI, applies radio waves and strong magnets to produce 3D images of the structure of the brain. By applying this method, F. Xavier C. Castellanos, MD, and colleagues showed in a study published in the Journal of the American Medical Association in 2002 that ADHD patients have approximately 3 percent smaller brains than the healthy controls. Moreover, MRI has also shown that the brain maturation rate is approximately three years slower in children with ADHD than in the healthy controls. These findings were published in a National Institute for Mental Health report in 2007.
Positron Emission Tomography
Positron emission tomography, or PET, is a nuclear medicine tool that uses small amounts of radioactive material to study brain activity in certain areas. Some neurotransmitters that send messages from one neuron to another have been linked to ADHD. One of these is dopamine. Dr. Thomas Spencer and colleagues used PET to study dopamine regulation in ADHD patients and control subjects. They found abnormal dopamine transporter binding in the striatum of the ADHD patients. The study was published in the Biological Psychiatry journal in November 2007.
Functional Magnetic Resonance Imaging
Functional magnetic resonance imaging, or fMRI, applies the paramagnetic properties of oxygenated and deoxygenated hemoglobin to study how the blood flows in certain brain areas as a result of increased neural activity. fMRI has been employed to study the impulsiveness in ADHD patients. In their fMRI study, K. Rubia, Ph.D. and colleagues used a "stop" task that requires inhibition of an already planned motor response. They reported that ADHD children responded prior to stimulus onset, and showed a lower probability of inhibition than their healthy controls. Moreover, the children with ADHD were slower in their reactions than their healthy controls. The study was published in the British Journal of Psychiatry in 2001.
Magnetoencephalography
Magnetoencephalography, or MEG, measures the magnetic fields that are produced by electrical activity in the brain. It is closely related to electroencephalography, or EEG, which measures the electric potentials generated by neurons instead of their corresponding magnetic fields. The skull and tissue affect the EEG, however, but they have no effect on MEG. The prescription of methylphenidate, or MPH, has been shown to be effective in 75 percent to 90 percent of ADHD patients. There are still some patients who cannot be helped with this medication, says Christian Wienbruch, Ph.D. and colleagues, in a study that was published in the BioMed Central Psychiatry journal in July 2005. The medication increased activation in the frontal areas of most of the ADHD patients. The authors stated that MEG could be used to identify patients who are good or bad responders of MPH before they are treated with amphetamines.
References
- TThe ADHD Report Journal": Recent Developments in the Neuroimaging of ADHD
- National Institute of Mental Health: Brain Matures a Few Years Late in ADHD, But Follows Normal Pattern
- JAMA: Developmental Trajectories of Brain Volume Abnormalities in Children and Adolescents With ADHD
- BMC Psychiatry: The Influence of Methylphenidate on the Power Spectrum of ADHD
- The British Journal of Psychiatry: Neuropsychological Analyses of Impulsiveness in Childhood Hyperactivity
