Researchers do not entirely agree on definitions of the executive functions and where they are in the brain. The researchers are using methods like PET scans and M.R.I.'s to map their locations. But clearly much of the action is in the highly developed frontal lobes, the area that makes up one-third of the cerebral cortex in humans, and other structures with links to it.

The cat, by contrast, gets by with frontal lobes amounting to just 3.5 percent of its cortex, said Dr. Kirk Daffner, a neurologist at Brigham and Women's Hospital in Boston. That may not come as a total shock to cat owners, watching their pets meander aimlessly from chair to food bowl to sunny spot.

The frontal lobes are, unfortunately, extremely vulnerable to injury or disease. Car accidents and other head injuries are major causes of executive losses in younger people, and executive functions are among the first to be eroded by Alzheimer's disease.

Genetic factors probably have a role. The disorder can run in families.

Dr. Russell A. Barkley, a psychologist at the Medical University of South Carolina in Charleston, who is an A.D.H.D. researcher, said he believed that attention disorders and impaired executive function stemmed from a developmental flaw in the self-regulation mechanism of the brain. Because the nerve pathways in the frontal lobes are the last in the brain to mature, executive functioning is not fully developed until people are in their 30's.

No single test measures the strength of executive functions. Instead, neuropsychologists use batteries of tests to evaluate performance in a number of areas.

One area is inhibition, a basic and vital function that enables someone to delay automatic responses to stimuli, thoughts and changes in the environment. It allows an instant to consider consequences before acting, avoiding mistakes and bad decisions. For example, the Stroop Test displays lists of color names printed in colors that do not match the names. Directed to reel off the actual colors, most people mistakenly say the written word, unless they inhibit that automatic response.

Another field for testing is shifting, maintaining attention to a task, but smoothly switching, if necessary. Such transitions are difficult for people with executive dysfunction, and so are tolerating changes in environment and thinking flexibly in solving problems.