Twin studies in ADHD demonstrate a significant genetic contribution to the disorder. Linking this genetic influence to specific biomarkers may provide a better understanding of the pathophysiology of ADHD. Grainne McLoughlin and colleagues at the University of California San Diego and King's College London recently published a twin study of brain EEG and the genetics of ADHD. In their study 67 twin pairs (34 monozygotic and 33 dizygotic) between the ages of 12 and 15 years completed tasks measuring brain frontocentral EEG theta patterns and reaction time. Brain EEG frontocentral theta EEG levels increase under tasks requiring cognitive control, reaction time and handling reaction under conflict. The authors were able to identify a specific type of EEG response in twins with ADHD compared to twins without the disorder.
Twins without ADHD showed changes in reaction time variability (RTV) and EEG theta performance with an attention and reaction task.
Twins with ADHD showed no change in these measures with the same attention and reaction task.
Of note, the authors were able to link this specific RTV and theta response to genetic features contributing to ADHD. The authors note in their conclusion:
"This is the first finding that confirms the genetic link between frontal midline EEG activity and ADHD, as previously suggested by family studies."
This is an important finding and has significant implications in:
Furthering understanding an EEG evoked response that may assist in the diagnosis of the ADHD phenotype
Provide a biomarker for future family, twin and genome-wide genetic studies of ADHD
Be helpful in teasing out environmental from genetic factors in ADHD
Readers with more interest in this study can access the free full-text manuscript by clicking on the PMID link in the citation below.
Photo of wood stork in flight is from the author's files.
There are a variety of methods to study the effects on exercise on brain function. Brain imaging techniques such as fMRI provides a new tool to search for regional effects of acute and chronic exercise. Another tool that has received less attention is the electroencephalogram or EEG. One EEG measure of brain function is the individual alpha peak frequency or iAPF. The iAPF is positively correlated with arousal, attention and speed of information processing. Higher iAPF is linked to faster speed of information processing. Boris Gutmann and colleagues from the German Sport University Cologne recently published a study of the effects on acute and chronic exercise on iAPF. Here are the key elements in the design of their study:
Subjects: Ten males average age 22 who were regular participants in exercise but not highly trained endurance athletes
Exercise: Time1- iAPF before and after exhaustive exercise and before and after steady state. Time2-iAPF before and after exhaustive exercise and before and after steady state. Time 1 and Time 2 exercise sessions were separated by four weeks that included steady state aerobic exercise training
The key findings from the study were:
iAPF was increased after exhaustive exercise but not following steady state exercise
This effect occurred both at time 1 and time 2 suggesting it was independent of training
The authors note the arousal effect of exhaustive exercise may be "mediatede by changes in neural activity in the reticular-activating system". I found it interesting that the effects of iAPF was limited to exhaustive exercise. In the exhaustive exercise protocol, subjects rode stationary bikes controlled by the researchers for intensity. Subjects started at 30 watts increased by 5 watts every 30 seconds until subjects reached exhaustion. The steady state exercise protocol was exercise on the bicycle for 30 minutes at 65-75% of maximal heart rate. There appears to be some increasing research interest in the value of shorter periods of exhaustive exercise like that seen in interval training protocols. Increasing evidence supports the value of brief high intensity periods of exercise in promoting health benefits of exercise. Using EEG markers may be helpful in examining the potential value of exercise in a variety of brain disorders, i.e. traumatic brain injury, attention deficit disorder, mood and anxiety disorders. Readers with more interest in this study can access the free full-text manuscript by clicking on the PMID link below. Photo of Captiva, FL sunset is from the author's files. Follow the author on Twitter: @WRY999 Gutmann B, Mierau A, Hülsdünker T, Hildebrand C, Przyklenk A, Hollmann W, & Strüder HK (2015). Effects of physical exercise on individual resting state EEG alpha peak frequency. Neural plasticity, 2015 PMID: 25759762
TED presentation by Dr. Aditi Shankardass brings up an important question--should all children with autism (or those undergoing an assessment for autism) have an EEG. The presenter notes that in her experience in India, up to 50% of children referred with a diagnosis of autism have a seizure disorder or some other neurodevelopmental disorder. The TED talk is posted above (7 minutes) and here are my notes from the presentation.
1 in 6 children suffer from developmental disorder
Most diagnosed solely on symptoms
Accuracy of diagnosis improved with laboratory measures
Technology holds hope for diagnosing brain disorder
She worked in a Harvard lab studying mathematical models to measure brain activity
Statistical probability mapping combines EEG and statistical science
She is setting up this technology in India
Case study--seven year old referred with a diagnosis of autism
EEG study was quite helpful
Child did not have autism but had a seizure disorder
Antieplileptic medication resulted in dramatic improvement
She has found a significant number of children diagnosed with autism that had seizure disorders in the Indian referral population, this may be up to 50% of cases
So what about assessment guidelines for autism in the United States and Europe? One of the best autism guidelines I could track down came from the Scottish Intercollegiate Guidelines Network. This free guideline pdf document can be located here. The guideline is titled: "Assessment, diagnosis and clinical interventions for people with autism spectrum disorders. A national clinical guideline".
The guidelines provide a comprehensive review of the evidence supporting a variety of measures in the assessment process. The recommendation from the guideline related to standard EEG assessment is summarized: "Whilst epilepsy is common in children with ASD, there is no indication for an electroencephalogram (EEG) in the absence of other clinical criteria." This recommendation comes with a citation from a 2005 review article by Kagan-Kushnir.
This review notes that seizures occur in 20-30% of children with autism and EEG abnormalities have been found in 10 to 72% of study samples. Subclinical EEG abnormalities have been found in 6-30% of samples. The authors note "There is insufficient evidence to recommend for or against the use of screening EEGs in autistic patients. Given the frequency of seizure disorders in this patient population, a high index of clinical suspicion should be maintained for subtle symptoms of seizures".
The EEG technique referenced by Dr. Shankardassappears to be quantitative EEG or qEEG, a more complex EEG analysis than that done in a clinical setting. qEEG research is ongoing at the TRANSCEND Research laboratory at Harvard directed by Dr. Martha Herbert. Dr. Herbert and colleagues have investigated a variety of EEG research measures in autism. Recent findings indicate that autism subjects show decreased synchrony between the right and left brain hemispheres. The clinical implications of these findings are unclear at this point.
It is unlikely that the percentage of undiagnosed clinically significant seizure disorders in autism in developed countries is high. Nevertheless, clinicians and parents should be alert to potential subtle and non-subtle signs of seizure disorder in those with autism. Additionally, it is not common for a child diagnosed with epilepsy to be misdiagnosed as autistic and to be "cured" by anti-epileptic therapy in the U.S. or Europe. Although not unheard of, this misdiagnosis is reduced with comprehensive multidisciplinary assessments. Concurrent autism and epilepsy (and EEG abnormalities) is a more likely clinical scenario than one disorder being misdiagnosed an the other.
The clinical diagnosis of autism and differential diagnosis of epilepsy continues to be one made primarily by careful history, observation and application of diagnostic criteria. Although this approach is not perfect, it does approach the reliability and validity found for other common medical conditions. When applied in a multidisciplinary setting, this approach is unlikely to misdiagnose a child with epilepsy as having autism alone.
So I think the question of need for an EEG in the context of autism should be left to the discretion of the managing physician. Many will need an EEG as part of the assessment and differential diagnosis. Some may not need them and the the managing physician is best able to make this distinction.
Kagan-Kushnir T, Roberts SW, & Snead OC 3rd (2005). Screening electroencephalograms in autism spectrum disorders: evidence-based guideline. Journal of child neurology, 20 (3), 197-206 PMID: 15832609
Isler JR, Martien KM, Grieve PG, Stark RI, & Herbert MR (2010). Reduced functional connectivity in visual evoked potentials in children with autism spectrum disorder. Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology PMID: 20605520
