"If you, your child, or a loved one has Attention Deficit Hyperactivity Disorder, or ADHD, you already know that it’s a challenging disorder that affects memory, attention, and behaviour. 
It’s now believed that ADHD doesn’t have a single cause—rather, it’s probably due to a combination of multiple genetic and environmental factors. There is no specific brain scan or blood test that confirms a diagnosis of ADHD; however, we do know that some portions of the brain are typically smaller, while some studies conducted in children with ADHD showed a delay in maturation.
The particular area of the brain that’s most affected appears to be the prefrontal cortex, located just behind the forehead. This part of the brain is crucial for many of our basic thinking functions: it’s the control centre that enables us to organize, plan, pay attention, make decisions, and so on—as this detailed list shows.
• Problem solving
• Memory
• Language
• Motivation
• Judgment
• Impulse control
• Social behaviour
• Planning
• Decision-making
• Attention
• Ability to delay gratification
• Time perception
Certain brain chemicals, called neurotransmitters, are known to play a role. Among others, dopamine and norepinephrine are two key neurotransmitters that, when present at the correct, balanced levels in the brain, contribute towards maintaining alertness, increasing focus, and sustaining thought, effort, and motivation."