You've known of children who are hyperactive - those kids who don't seem to listen or to follow through on tasks; who are easily distracted, impulsive, and moody; and who are always "on the go."

But what you may not know is that hyperactive children often become hyperactive adults, plagued in adulthood by the same symptoms that caused them grief in childhood. That, in fact, may be the case in one-third to two-thirds of these instances, says Paul H. Wender, M.D., author of "The Hyperactive Child, Adolescent, and Adult" and director of psychiatric research at the University of Utah Medical Center."Of course, the criteria of throwing spit balls, talking in class, of not being able to wait their turn in games don't apply to 50-year-olds," Wender notes. Instead, the child who experienced these problems becomes the "fidgety" adult - still in constant motion - who may continuously squirm in his chair, tap his fingers, or jiggle his feet.

The child who couldn't concentrate on fractions becomes the adult who can't concentrate on the income tax form. The child who had an untidy room, unfinished assignments and careless reading and writing becomes the child who carries this disorderliness and disorganization into the home front or work place, with consequent difficulty in solving problems, structuring time and sticking to tasks.

Finally, the child who couldn't tolerate delays or frustrations, who was apt to sock his siblings or classmates if they didn't do what he wanted, becomes the adult who has unstable, stormy and often failed relationships. Beset by impulsivity, and mood and temper problems, such an adult often initiates and terminates relationships without thoughtful reflection.

Hyperactivity, and the group of traits associated with it - inattentiveness and distractibility, impulsivity, restlessness, demandingness, perceptual and learning difficulties and social aggressiveness - in large part are biologically caused, Wender stresses.

As a "genetically determined disorder," hyperactivity produces deficiencies in some neurotransmitters, or chemicals, in the brain. Describing the difficulty that occurs when chemical deficiencies are present, Wender relates: "One nerve cell releases a small amount of certain chemicals, which are picked up by a second cell, causing it to `fire'. . . . If there is too little of a particular neurotransmitter, the second cell will not fire because not enough of the neurotransmitter has been released by the first cell." Thus, the chemical connection between nerve cells is broken.

Because hyperactivity is caused by deficiencies in the brain's chemicals, in the majority of cases this disorder responds to medication, notes Wender. People often make appreciable, even dramatic, improvements: "They slow down, become relaxed, are able to concentrate, and can deal much more effectively with stress. Their distractibility is relieved, the high and low periods go away, outbursts of aggression and anger disappear, organization improves and impulsivity and aggression decline."

With medication, people then become more amenable to psychological therapies, Wender says. They can take time to repair damaged relationships, to adopt new communication techniques and to remedy failures at work, school or home.

Wender, who is a pioneer in the assessment and treatment of hyperactivity, has obtained with colleagues a grant from the National Institute of Mental Health to study adult hyperactivity. At present, researchers are soliciting volunteers for this study who fit the following criteria: adults over the age of 25 who have been hyperactive as children and continue to show hyperactivity as adults, including lifelong problems with restlessness, inattentiveness, impulsivity, overactivity, and trouble managing moods, temper and stress.

Because hyperactive adults are often imperceptive concerning their own symptoms, or even to the "profound leaps upwards" they may experience with medication, participation in the study requires that a "significant other" also participate as an observer. The wisdom of this requirement is reflected in the example of a wife, who, after her husband reported to Wender he was "slightly improved" with medication, commented: " `Slightly improved' is like being married to a different man."

Free diagnosis and treatment for adults meeting the above criteria is available through the Hyperactivity Research Clinic, University Medical Center. Wender stresses that people who do not respond to treatment will be rediagnosed and referred to appropriate or private agencies for treatment of problems.

If you're a hyperactive adult and think you might benefit from getting symptoms under control, obtain more information by calling 581-8075. Making that call could change your life.