The Reticular Activating System, and its Role in Attention Deficit Hyperactivity Disorder

In our last article about the neurology of ADHD we began to introduce the reader to the system in the brain known as 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 that 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. But 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 under-aroused 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 see individuals with excessive startle responses, hyper-vigilance, 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. 
 
What factors could cause the Reticular Activating System to be either over-activated or under-activated? 

According to Harvard Medical School, current research strongly suggests that Attention Deficit Disorder is caused in part 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 under-aroused ADD kids, and somewhat well for the over-aroused impulsive-hyperactive ADHD kids.

However, for the kids who have an over-aroused Reticular Activating System to begin with, the use of stimulants will often exacerbate the problems with temper, sleep, and hyper-vigilance or anxiety. For these individuals their physicians will often prescribe a Norepinepherine antagonist such as Clonadine, or an antidepressant such as Prozac, which works to enhance the Serotonin driven inhibitory mechanisms of the brain.

However, it is not just activation levels of the Reticular Activating System that are a problem with Attention Deficit Disordered individuals.

It seems that the same problems that cause the Reticular Activating System to be under or over aroused also restricts the development of neural connections and the required neural density needed to process incoming information. In other words, these are issues with the number of brain cells, the size of the brain cells, and the number of connections between brain cells. It is not uncommon for one brain cell to have as many as 5,000 connections with other brain cells.

Picture the incoming information to be processed and learned as the volume of water coming out of your shower head. And picture the brain's ability to process this information as the drain and the drain pipe in the shower floor. If the pipe is clogged up, your shower will have problems draining. If the contractor originally installed a drain pipe that is too small, again your shower will have problems draining. In either case, you will either have to reduce the amount of water coming out of the shower head, or you will have to let the shower back up and wait a while for the water to finally drain out. Here's the connection?

If the brain does not have enough neural connections, or lacks the neural density, to process the incoming information, then it will be like a pipe that is too small to handle a large volume of water. It will take in some, but the rest will be stopped and won't go down the pipe rapidly. Learning will take place, but the time that it takes to process the information will be slowed significantly. 

The impact of this with an Attention Deficit Hyperactivity Disorder child is best seen when the child is given a timed test, even with material that the child understands pretty well.

The "timed" aspect of the test requires that the child have a "larger drain pipe," as it were, to quickly process the problems on the test and recall the answer. However, with Attention Deficit Disorder - ADHD - the "pipe" is often too small, and the results of the timed test will probably be very poor. However, take away the timed element on the same test, and "allow the water to drain a the slower rate," and the child will often do well on the test.

So the ADHD child, or adult, needs to develop a greater degree of neural density, and a larger number of neural connections to process information faster and more efficiently.

Now, please do not think that this information to be processed is only what takes place in the classroom. The information to be processed includes information from the outside world, including the touch of the clothes on his skin, the buzz of the lights overhead, the sound of the kids playing outside, and the new information that the teacher is lecturing on at the front of the classroom. It also includes the information from inside the head, the thoughts and feelings of the ADHD person.

All of that must be sorted out and filtered, so that only the important information is paid attention to, and the unimportant information is ignored. Without proper filtering by the Reticular Activating System, the individual will be distracted by "noise," both from outside of him as well as from inside of him. You can learn more about the neurlogy of Attention Deficit Hyperactivity Disorder by reading through the ADHD Information Library.

Douglas Cowan, Psy.D., is a family therapist who has been working with ADHD children and their families since 1986. He is the clinical director of the ADHD Information Library's family of seven web sites, including http://www.newideas.net, helping over 350,000 parents and teachers learn more about ADHD each year. Dr. Cowan also serves on the Medical Advisory Board of VAXA International of Tampa, FL., is President of the Board of Directors for KAXL 88.3 FM in central California, and is President of NewIdeas.net Incorporated.