Attention-deficit hyperactivity disorder (ADHD) is a neurological disorder that may be characterized by the presence the following symptoms (among many others)[1]:
· Problems focusing on a specific task
· Trouble sitting still for long periods of time
· Being disorganized
· Inability to follow instructions
· Impulsivity
The Role of Dopamine and the Prefrontal Cortex
The part of the brain that regulates such activity is called the prefrontal cortex (PFC). The PFC requires sufficient amounts of dopamine to function correctly, especially in focus maintenance and learning. The pathway in which dopamine is transported from a part of the midbrain known as the SN/VTA to the PFC, is called the mesocortical system.
The hypodopaminergic theory of ADHD states that hyperactive behaviors and lack of attention associated with ADHD may be the result of low dopamine levels. Dopamine and glutamate maintain a feedback loop involving the PFC. When low dopamine levels are present, dopamine is no longer able to increase the function of glutamate receptors (NMDA and AMPA) in the PFC and striatum, leading to lower glutamate levels. In a healthy cycle, glutamate signals are sent to the striatum and the SN/VTA, as well as to the PFC. Normally, when glutamate signals to the SN/VTA are increased, more dopamine is released, restarting this cycle. This feedback mechanism does not appear to occur in patients with ADHD.[2]
ADHD and Reward Systems
Attention deficits may also stem from lack of motivation to complete a task. Patients with ADHD have been found to require stronger incentives and prefer smaller, more instant rewards, as opposed to larger, more distant rewards.[3][4][5] While dopamine is important for optimal PFC function, it is also important in what is known as the mesolimbic pathway. This pathway connects the VTA to the nucleus accumbens (NAcc), and is responsible for reward systems, which relies heavily on dopamine. Disruptions in this pathway have been linked to the presence of ADHD.[6]
A More Natural Approach
ADHD is typically treated with pharmacological interventions, including stimulant and nonstimulant drugs. For a more natural approach, consider measuring dopamine and glutamate levels. Also, for a list of natural remedies that have been proven effective in improving ADHD related symptoms and more detailed information on dopamine’s role in the PFC, check out our blog “ADHD: Can we address this brain chemistry?”
References
[1] Centers for Disease Control and Prevention (April 29, 2016). Attention-Deficit/Hyperactivity Disorder (ADHD). Retrieved from http://www.cdc.gov/ncbddd/adhd/facts.html.
[2] Erin M. Miller, Theresa C. Thomas, Greg A. Gerhardt and Paul E. A.
Glaser. 2013. Dopamine and Glutamate Interactions in ADHD: Implications for the Future Neuropharmacology of ADHD, Attention Deficit Hyperactivity Disorder in Children and Adolescents, Dr. Somnath Banerjee (Ed.), InTech, DOI: 10.5772/54207.
[3] Kollins SH, Lane SD, Shapiro SK. The experimental analysis of childhood psychopathology: a matching analysis of the behavior of children diagnosed with attention deficit hyperactivity disorder. Psychol Rec 1997; 47: 25–44.
[4] Sonuga-Barke EJ. The dual pathway model of AD/HD: an elaboration of neuro-developmental characteristics. Neurosci Biobehav Rev 2003; 27: 593–604.
[5] Tripp G, Wickens JR. Research review: dopamine transfer deficit: a neurobiological theory of altered reinforcement mechanisms in ADHD. J Child Psychiatry 2008; 49: 691–704.
[6] Volkow ND et al. Motivation deficit in ADHD is associated with dysfunction of the dopamine reward pathway. Molecular Psychiatry 2011; 16: 1147-1154.
Clinical Contributor
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