Typically, young children have what are known as subtle neurological signs. These are involuntary movements of one part of the body that occur while the child is making a voluntary movement of another part of the body. This is referred to as synkinesis, or overflow movements. These overflow movements disappear during normal development and are usually gone by the age of 10. However, in children with ADHD these overflow movements tend to be more intense and last long after the age of 10. This leads researchers to believe there is an abnormality in the maturation and development of the brain areas associated with motor activity in children with ADHD.