PET SCANS IN ADULTS
In men who had ADHD, PET scans showed that they processed a memory task in visual areas in the occipital lobe of the brain, as indicated by the yellow spots in the left image. Non-ADHD men used the temporal and frontal lobes, shown at right (ABCNEWS.com)
MRI OF ADHD BRAIN
MRIíS give detailed volumetric measurements of specific regions of the brain.
The volumetric measurements of the caudate nucleus indicate a smaller right caudate nucleus in ADHD
boys in comparison to normal boys
Extensive and time consuming measurements of the head and body of the caudate nucleus and the frontal lobes have supported their role in ADHD
NEURO SPECT SCAN
The Lancet November 22, 2003
Shedding light on ADHD
Brain-imaging study sheds light on ADHD
Brain-imaging study sheds light on ADHD Authors of a US study published this week provide details of the underlying physical causes of attention-deficit hyperactivity disorder. Using high resolution MRI and surface-based computational image analytical techniques, Elizabeth R Sowell and colleagues noted that patients with attention-deficit hyperactivity disorder had reduced regional brain size in inferior portions of dorsal prefrontal and anterior temporal cortices bilaterally. They also recorded large increases in grey matter in large portions of the posterior temporal and inferior parietal cortices.
Brain Scans Shed Light on Attention Disorder
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LONDON (Reuters) - Scientists said on Friday they have uncovered new clues about the underlying cause of attention deficit/hyperactivity disorder (ADHD), which affects up to six percent of children in the United States.
In Using high-resolution magnetic resonance imagining (MRI) scans, Elizabeth Sowell, a professor of neurology at the University of California Los Angeles, and her colleagues found differences in areas of the brain linked to attention and impulse control in children with ADHD.
The disorder is characterized by impulsive behavior, a poor attention span and inability to sit still, follow instructions and complete tasks. There is no cure but medication can decrease the symptoms, along with tutoring and behavioral therapy.
"These findings may help us understand the sites of action of the medications used to treat ADHD, particularly stimulant medications," said Bradley Peterson, an associate professor of psychiatry at Columbia University, who worked on the research.
Peterson said the findings, which are reported in The Lancet medical journal, could help to develop new treatments.
The researchers compared MRI scans of brains of 27 children and adolescents with ADHD and 46 others. The ADHD children had changes in brain structure in certain areas of the brain.
"The changes are not only in brain regions controlling attention, but also in regions that subserve impulse control. Disordered impulse control is often the most clinically debilitating symptom in children with ADHD," Peterson added.
Brain Image Scanning & Mapping with AD/HD An Overview
Brain Imaging in ADHD
Position Emission Tomography (PET)
Single Photon Emission Computed Tompgraphy (SPECT)
For a long time researchers have tried to pinpoint the seat of ADHD in the brain. Initially they used the brain wave test, electroencephalogram (EEG), but this mainly detected abnormalities in the superficial layers called the cortex and did not tap into the deeper parts. Methods such as CT and basic MRI scans showed up the anatomy of the brain but in ADHD there were no significant lesions. In the late 1980's new types of scan became available, which could reflect brain function. The SPECT (Single Photon EmissionComputed Tomography) and PET (Positron Emission Tomography) scans look at blood flow and metabolism in different parts of the brain. This is able to indicate the areas that are being relatively over or under used. With SPECT and PET scans it was found that regions located centrally and deep within the brain (called caudate nuclei/striatum) were the most consistent areas of under-function in ADHD, as were the frontal lobes and the posterior rperiventricular region. In the SPECT and PET scans blood flow and glucose metabolism to these areas were low, which reflected reduced activity.
The striatum, frontal lobes and posterior periventricular region are thought to be important for controlling and directing what we attend to. As well as having complex connections with each other, these three regious are richly interconnected with the sensory cortices, the regions of the brain that receive sensations. They act as a gate, allowing important information to register but filtering out the noise of interfering information which may prevent us from focusing on relevant messages. Because these 'gates' are under-functioning in ADHD they are unable to filter out the hundreds of important stimuli that arrive every minute. This constant, unchecked bombardment shows up in the sensory cortices. They become flooded with incoming messages and can be seen on the SPECT scan as high blood flow to the areas that receive vision and sound, the occupital and temporal lobes.
When methylphenidate (Ritalin) was administered to ADHD children, its effect showed up on Xenon-133SPECT as a redistribution of blood flow in the brain, methylphenidate sppeared to increase the level of function of the under-perfused regions at the striatum, posterior periventricular region and to a lesser extent the frontal lobes. This normalisation allowed the clutter of irrelevant messages to be screened out and was seen as a reduction in blood flow to the vision and hearing areas. This filtering of irrelevant distraction suppresses reflex responses and helps concentration.
More recent PET and SPECT scans have mostly (but not all) backed up these differences in regional metabolism. The changes in function described after the administration of Ritalin have not been conclusively replicated. That there is still conflict in the results obtained by different research studies may be accounted for by differences in the subtypes of ADHD, the presence of comorbid disorders and methodological differences inhereent in the use of these scans.
Magnetic Resonance Imaging (MRI)
Functional scans such as the SPECT and PET scans involve a high level of ionising radiation. This has limited studies in children using these imaging techniques. Now there is a new modality for this purpose, the functional MRI. In an MRI scan, a picture is constructed from the radio-signal that is emitted from atoms in the brain when a magnetic field is applied to it. There is no ionising raditiaon involved. Previosly MRIs were used only to study the anatomy of the brain. Now, try superimposing the change in the composition of the radio-signal caused by changes in metabolic activity, it is possible to map the regions of the brain involved in executing a particular clinical activity. Currently studies using functional MRI are investigating the areas of the brain that are involved when children are engaged in a continuous performance task (CPT) Early evidence indicates that this task, which requires inhibition of resoponses, is localised to the prefrontal lobes.
Another new use for the MRI is for detailed volumetric measurements of specific regions of the brain. Extensive and time consuming measurments of the head and body of the caudate mucleus and the frontal lobes have supported their role in ADHD. The volumetric measurements of the caudate nucleus indicate a smaller right caudate nucleus in ADHD boys in comparison to normal boys. The usual "right greater than left" caudate asymmetry was reversed in ADHD. The frontal region of the brain was smaller and the normal age-related changes in the volumes of the caudate and lateral ventricals were absent in this condition.
In summary The findings from structural and functional studies are in agreement with each other and with earlier neurocognitive studies in the localisation of ADHD to the fronto-striatal circuit. There are rich dopaminegic connections between the frontal/prefrontal regions and the caudate/striatal regions. Advances in the field of neuroscience suggest the executive functions, inhibition, intention and active working memory are the cognitive deficits underlying ADHD. The frontal and striatal circuits have been demonstrated to subserve such executive functions, this being shown by a wide body of researchers (see Appendix XVI, Goldman-Rakic).
Quantitative EEG - Brain Mapping
The standard electroencephalograph (EEG) measures brain electrical activity. Tracings are made from electrodes placed around the skull. The resulting paper record is read by a neurologist who will note major abnormalities which suggest conditions such as epilepsy. This technique is too crude to pick up the subtle electrical differences present ADHD.
QEEG brings computer technology to this old EEG method. Quantative diagnostic features are extracted from the standard EEG, cortical evoked potentials and brainstem evoked potentials to give an objective statistical evaluation of brain electrical activity. The results of this evaluation are represented by coloourful maps and tables of data which highlight areas of activity that stand out as different from what would be expected for the average child of the same age.
The technique is available for children aged sicx years and older. It is non-invasive, painless and unlike other scans, can cope with some movement in the restless child.
Brainwaves are recorded from electrodes placed at standardised sites on the head. The electrodes are attached to a special cap which is fitted on the child. Data are collected in two main ways. Firstly, data are recorded from EEG tracings as the child sits quietly with eyes closed. Next, brainwave activity is collected while the child is presented with various stimuli. Flashes of light, checkerboard pattern reversals and tones or beeps are presented while measuring cortical evoked potentials. Loud clicks at 80 decibels are used while recording brainstem auditory evoked responses.
One expects to see certain patterns of response to the 'average' child or adult. The areas where the dysfunctions occur give an indication of the anatomical and electrical messages that reach the outside of the skull. This may not accurately measure subtle activity deep in the brain.
In the child with ADHD there is a slowing of the brainwaves which appears most prominently in the frontal regions. In children with specific reading disability certain patterns of functioning are observed which deviate from normal. Children with primarily auditory difficulties show different patterns to those with poor visual processing.
By providing a quantitative estimate of the maturational level of the brain and adequacy of information processing, one can document changes that come with medication and maturity.
QEEG is relatively new to the fields of paediatics and neurology. There are a number of clinics worldwide utilising this in the assessment of ADHD reading disability and various paediatric disorders.
In Australia one trademark package of QEEG, Neurometrics, was popularised by the late Dr. Gordon Serfontein. He saw this as an objective indicator of these imprecise conditions that were otherwise hard to document. Dr. Serfontein's views were not universally accepted by his colleagues.
Current research is focusing on the use of QEEG in cognative disorders, both in children and in adults. We have do doubt that this has a place in the diagnosis and monitoring of ADHD. Whether this is just another pointer towards the diagnosis or something far more specific, time will tell.
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