Research linking biology and behavior continues, and some noteworthy recent findings are summarized below. Dopamine, one of the many neurotransmitters found in the brain, is strongly linked to pleasure and sensation seeking. Previous studies on animals and human twins indicate that novelty-seeking behavior is evenly attributable to genes and the environment.
Boys are twice as likely to be affected as girls.
Many children with ADD have learning disabilities and exhibit disruptive behaviors. Some psychiatrists claim that 2 million children in the United States have ADD and have put more than a million people on Ritalin. Clinicians do not understand what causes ADD, nor do they understand the mechanism of action of Ritalin, which some critics charge is misprescribed and overprescribed. Researchers from University of California at Irvine reported recently in the Journal of Molecular Psychiatry that the D4 dopamine receptor contains a unique segment that repeats itself seven times in half of the ADD children and only in 21 percent of the control group. In addition, children with the sevenfold reptition have a more severe form of ADD than children with other forms of the gene.