Looking for the differences in brain activity with attention deficit disorder in children is extremely important, not only for parents, but also teachers, physicians, psychologists, psychiatrists, and researchers.
The distractibility, impulsivity and inability to concentrate don’t come from a desire to misbehave. Instead, children with Attention Deficit Disorder (ADD) are literally physically unable to exert the same level of concentration that children without ADD can use. When you tell your child with ADD not to run across the street without looking both ways; when you tell your child not to jump off the roof of your house, he’s not able to follow that direction because his brain is lacking in hormones and structures that allow him to think about his actions before he acts on them.
Tissues in Striatal Region
Researchers have discovered a difference between a brain with ADD and a brain without ADD. Dr. Glenn Austin and Dr. Hugh Ridlehuber, and a school psychologist Gary Kirkorian, from the Community/Academia Coalition of Los Altos, California; along with Gary Glover and John Desmond from the Stanford Medical Center’s Radiology Department, worked on a study looking for physical differences in brain activity with attention deficit disorder.
These researchers used functional magnetic resonance imaging (FMRI) in completing their work.  The study took 16 boys, aged eight to 13 and took images of their brains as they played a mental game. Each boy was lying in a magnetic resonance imaging device, having the front portion of his brain (frontal-lobe cortex and striatal structures under the frontal-lobe cortex). Each boy was told to press a button when they saw any letter but X flash on a display screen. Each child developed a predisposition to press the button and had to control his impulse to press it even when he saw the X flash by.
After the imaging was complete, the researchers studied the brain scans. They found a noticeable difference in how neuronal tissue in two structures of the striatal region activated themselves.
The test was conducted one more times after each child (with and without ADD) had taken a dose of Ritalin. The differences in the boys’ brains was even more marked after taking medication, according to Science Daily. 
The boys diagnosed with ADD exhibited more brain activity in the striatal structures when they took Ritalin than when they were unmediated. In contrast, the boys without ADD shows less activity in the striatal region after taking Ritalin.
Activity in Caudate and Putamen after medication
The boys in the study showed more brain activity in the putamen and caudate structures (in the striatal region) after they took a dose of Ritalin. 
According to Science Daily, Ritalin’s primary action influences the neurotransmission of dopamine. Because Ritalin has an opposite, or paradoxical, effect on the brains of boys with ADD, researchers believe ADD “involves atypical dopamine modulation in the striatum", as stated by Research Associate Chandan Vaidya and Associate Professor John Gabrieli, of Stanford’s Department of Psychology. 
Prefrontal Cortex Activity
Children with ADD have altered activity in the prefrontal cortex, which is called the “command center” of the brain. Because of this altered brain activity with attention deficit disorder, their ability to control their impulses is impaired, according to the University of Maryland Medical Center. 
Science Daily: Differences in Brain Function Found for Attention Deficit Disorder
University of Maryland Medical Center: Attention Deficit Hyperactivity Disorder