The Neurobiological Origin of ADHD
Attention deficit hyperactivity disorder (ADHD, a term that includes what was formerly known as attention deficit disorder or ADD) is a growing problem in America. The American Psychological Association (APA) added the condition to its diagnostic handbook, the Diagnostic and Statistical Manual, in the late 1980s.
The latest edition says that about five percent of American children have ADHD, but research indicates that number is much higher. According to one study, as of 2011, about 11 percent of children between the ages of 4 and 17 have ADHD. Over the past few decades, the rate of diagnosis has risen rapidly, increasing an average three percent per year from 1997 to 2006 and five percent per year from 2003 to 2011.
There are many potential reasons for the rise in diagnosis over the past few decades. It could be that awareness and understanding about the disorder has led medical professionals and educators to recognize the symptoms in more children. Alternatively, the modern way of life — including a largely sedentary lifestyle, an unhealthy diet filled with sugar, a decrease in the allotted time for recess and physical education in school, video games and other media — could be to blame. Some people also believe many medical professionals overdiagnose the condition and that many children diagnosed with ADHD are just exhibiting normal behavior.
While the average age at diagnosis is seven, ADHD is not a disorder that only affects children. ADHD often persists through adolescence and into adulthood. About 60 percent of patients diagnosed with ADHD as children will continue to have symptoms as an adult. About four or five percent of adults have ADHD, but fewer than 20 percent of the total are diagnosed and only about one-quarter of those diagnosed seek help.
ADHD can limit a person’s ability to succeed academically, socially and professionally. If a person does not learn to adequately handle the symptoms — through medication, behavior modification, or other treatment methods — then he or she may not learn how to overcome the problems associated with ADHD. However, many facets of the disorder remain unknown, which limits the treatment options.
Although some underlying neurobiological causes of ADHD have been discovered, a team from the CNRS (French National Center for Scientific Research), University of Strasbourg and INSERM (French Institute of Health and Medical Research) recently discovered a potential neurobiological origin of ADHD. Experiments using mice found that hyperstimulation of a cerebral structure, the superior colliculus, causes the same behavior problems seen in those with ADHD. Findings published in the journal Brain Structure and Function report that researchers found an accumulation of the neurotransmitter noradrenaline in this area, which shows that this chemical mediator probably has a role in attention disorders as well.
The superior colliculus is located in the midbrain area, and its main role is to receive data from the retina. It is also the sensory hub involved in controlling attention and visual and spatial orientation, integrating multi-sensory information and tracking objects in the field of vision. Experts have suspected that it may be involved in psychiatric conditions; however, prior to this study, its association with ADHD had not been demonstrated.
For the study, the researchers experimented on genetically altered mice with duplicated neuron projections between the superior colliculus and the retina. They compared the behaviors of different strains of genetically engineered mice and a control group in various behavioral tasks that require collicular activity.
The genetically modified mice had visual hyperstimulation and excess noradrenaline in the superior colliculus. Noradrenaline, also known as norepinephrine, acts as both a hormone and a neurotransmitter, and is associated with the “fight-or-flight” reaction in the body. Among other roles, it affects the mind’s ability to concentrate. An imbalance is associated with behavioral changes, including those characteristic of ADHD.
In this mouse study, the researchers found there was a loss of inhibition, demonstrated by the mice acting with less caution when entering a potentially hostile environment. They also showed more difficulty understanding relevant sensory information, and they acted impulsively. These patterns are similar to adults with ADHD.
Prior to this study, research into the neurobiological roots of ADHD relied mainly on animal models with disturbed dopamine production and transmission pathways. However, these pathways remained intact in the mice with a malformed superior colliculus. Therefore, this study demonstrated that there is another neurobiological reason for ADHD symptoms: dysfunction in the superior colliculus and regulation of noradrenaline levels.
This study broadens the understanding of the causes of ADHD, which could allow for a wider treatment approach for the disorder. Further research into the effects of noradrenaline on the superior colliculus could help experts develop innovative therapeutic strategies, including better medications than the stimulants currently prescribed for the disorder.
Friedman, J. (2014). The Neurobiological Origin of ADHD. Psych Central. Retrieved on March 31, 2015, from http://psychcentral.com/lib/the-neurobiological-origin-of-adhd/00019390