Reticular Activating System and "Attention Deficit Hyperactivity Disorder"
The next questions might be, then, What causes these various systems of the brain to get out of balance? Why would they become under aroused or over aroused as the case may be? Is there one central system that controls or regulates these other systems?
Let's turn our attention to the part of the brain called the Reticular Activating System. The Reticular Activating System is the attention center in the brain. It is the key to "turning on your brain," and seems to be the center of motivation. The Reticular Activating System is connected at its base to the spinal cord where it receives information projected directly from the ascending sensory tracts. The brainstem reticular formation runs all the way up to the mid brain. As a result, the Reticular Activating System is a very complex collection of neurons which serve as a point of convergence for signals from the external world and from interior environment. In other words, it is the part of your brain where the world outside of you, and your thoughts and feelings from "inside" of you, meet.
This Reticular Activating System is very capable of generating dynamic effects on the activity of the cortex, including the frontal lobes, and the motor activity centers of the brain. It plays a significant role in determining whether a person can learn and remember things well or not, on whether or not a person is impulsive or self-controlled, on whether or not a person has high or low motor activity levels, and on whether or not a person is highly motivated or bored easily.
The Reticular Activating System is the center of balance for the other systems involved in learning, self-control or inhibition, and motivation. When functioning normally, it provides the neural connections that are needed for the processing and learning of information, and the ability to pay attention to the correct task.
If the Reticular Activating System doesn't excite the neurons of the cortex as much as it ought to, then we see the results of an underaroused cortex, such as difficulty learning, poor memory, little self-control, and so on. In fact, if the Reticular Activating System failed to activate the cortex at all one would see a lack of consciousness or even coma.
What would happen if the Reticular Activating System was too excited, and aroused the cortex or other systems of the brain too much? Then we would probably see the individuals with the excessive startle response, hypervigilant, touching everything, talking too much, restless and hyperactive. So the Reticular Activating System must be activated to normal levels for the rest of the brain to function as it should.
According to Harvard Medical School, current research strongly suggests that ADHD is caused by a deficiency of Norepinephrine in the ascending reticular activating system, and it is thought that the stimulant medications, such as Ritalin, increase the levels of Norepinephrine in that part of the brain, as well as probably increasing dopamine levels in the frontal lobes. This treatment strategy works well for the inattentive ADD kids, and somewhat well for the overaroused ADHD kids. However, for the kids who have an overaroused Reticular Activating System to begin with, the use of stimulants will often exacerbate the problems with temper, sleep, and hypervigilance. For these individuals their physicians will often prescribe a norepinepherine antagonist such as Clonadine.
