Attention Deficit Disorder (ADD) is a dysfunction of the Central Nervous System (CNS), most specifically the Reticular Activating System, which results in difficulties of maintaining attention and concentration, learning and memory, as well as involving an inability to process and sort out incoming information or stimulus from both an individual's inner (subjective) and outer (objective) worlds. It may manifest itself in undue passivity or inattentiveness, or unruly, uncontrollable, aggressive hyperactivity in affected individuals.

The Reticular Activating System and its connections at the center of consciousness, attention, and learning.

It seems that the Reticular Activating System is intimately involved in the neural mechanisms which produce consciousness and focused attention, receiving impulses from the spinal cord, relaying them to the Thalamus, then to the Cortex, and back again in a feedback loop to the Hippocampus/Thalamus/Hypothalamus and the participating neural structures in order for learning and memory to occur. Without the continual excitation of cortical neurons by reticular activation impulses, a person is unconscious and cannot be aroused. When the stimulation is enough for consciousness, but not for attentiveness, Attention Deficit or Learning Disorders are the result. If too activated, a person cannot relax or concentrate and is over-stimulated or hyperactive, then that usually results in Attention Deficit Hyperactivity Disorder.