News: Specialized Press
A lower transmission of dopamine in the mesoaccumbens could be associated with symptoms of lack of attention typical of ADHD
Source: THE JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION (JAMA) 2009; 302(10):1084-1091. / Date: September 10th 2009 / Category: Specialized Press
Although for many years Attention Deficit Hyperactivity Disorder (ADHD) was considered a disorder for childhood and adolescence, it has been estimated to affect at least 3% to 5% adults, which makes it one of the most prevalent psychiatric disorder. Moreover, genetic and environmental factors that affect dopamine brain systems have been related to ADHD.
In agreement to previous studies, a deficit of dopamine may cause lack of concentration (especially in tasks that are considered boring or repetitive) and impulsivity. Both, along with hyperactivity, lack of motivation and deficits in receptivity to reward, typical symptoms of people with ADHD. This generates impaired responses characterized by a failure to delay gratification, impaired response to partial schedules of reinforcement, and preference for small immediate rewards over larger delayed rewards. These alterations in the reward pathway may explain, as stated by the authors, a greater risk of drug abuse in people with ADHD.
Just as it was revealed by a preliminary research, published by the 'Journal of the American Medical Association' (JAMA) and performed through brain images, a defective dopamine circuit, neurotransmitter of pleasant sensations, could be related with the symptoms of lack of attention displayed by people with ADHD.
Dr. Nora D. Volkow, of the National Institute on Drug Abuse of Bethesda, Maryland (U.S.A.) and her team, carried out an investigation in order to determine if there is abnormalities in the mesoaccumbens (the central area of the brain in which is located the reward pathway associated to dopamine) of patients with ADHD. The investigators obtained images through PET scans in order to measure the synaptic markers of dopamine (transporters and receptors D2/D3) in 53 non medicated adults with ADHD and 44 healthy controls.
According to the results, the authors consider that this research offers evidence of lower availability of receptors D2/D3 in people with ADHD in two key brain areas for “reward” and “motivation” (the accumbens and the middle brain). This explains the lack of response to reward coming from those patients
According to the investigators, the association between a lower transmission of dopamine in the mesoaccumbens and lack of attention, may have clinical relevance since this pathway has a key role in the association between reinforcement and motivation and in the stimuli-reward learning. Therefore, its involvement in ADHD supports the use of interventions to enhance the saliency of school and tasks to improve patients’ performance.
The authors believe that psychotherapy has shown to improve performance in ADHD patients. Also stimulant medications have shown to increase the saliency of a cognitive functioning such as motivation and interest.
Finally, the authors believe that this investigation provides preliminary evidence that the hypothalamus may also be affected by a lower availability of dopamine. If this fact is confirmed, future research may establish a neurologic base to explain the comorbidity of ADHD with signs and symptoms suggestive of hypothalamic pathology such as sleep disturbances, overweight and abnormal response to stress.