Adults have long worried about the younger generation's latest enthusiasms, and today more and wore of that concern is focused on computers and the Internet. In particular, the growing use of social networking sites is causing alarm among parents, educators and, increasingly, health experts.

The latest warning comes from Dr. Susan Greenfield, a noted British neuroscientist, who says sites such as Facebook, MySpace and Twitter are shortening attention spans, encouraging instant gratification, and making young people more self-focused.

Greenfield believes extended time using these sites is actually rewiring the brain. She told Britain's Daily Mail that, just as babies need constant reassurance that they exist, the networking Websites encourage the same impulse in teens.

My fear is that these technologies are infantilizing the brain into the state of small children who are attracted by buzzing noises and bright lights, who have a small attention span and who live for the moment, she told the newspaper.

Meanwhile, Taiwanese researchers suggest parents and educators pay more attention to childrens online habits because Internet-addicted teens seem more prone to aggression. However, Americans who study violence are not ready to make any conclusions about a possible link.

The study does not demonstrate that one behavior caused the other, said Dewey Cornell, a professor of education at the University of Virginia.

Even so, he said, other research shows that persons who play violent video games will be more prone to have aggressive thoughts, feelings and actions.

Internet addiction

Internet addiction itself remains a controversial topic more than a decade after it was first described. Some mental health specialists refuse to recognize its existence, although a number of rehabilitation centers treat people who say they suffer from it.

In the new study, researchers led by Chih-Hung Ko, M.D., from Kaohsiung Medical University, gave questionnaires to 9,405 adolescents and asked about their Internet activity and behaviors. The study appears online in the Journal of Adolescent Health.

The researchers deemed 25 percent of the male students and 13 percent of females to be Internet addicts based on a commonly used scale.

Thirteen percent of all female students and 32 percent of all males reported engaging in aggressive behavior — such as threatening or hurting others — within the last year, compared with 37 percent of those suffering from Internet addiction.

The researchers, who were not available for comment, wrote in the study that chatting online, playing video games and visiting sexually oriented Web sites could provide opportunities for teens to observe, experience and try aggressive behaviors resulting in positive outcome, such as identification in a group, being a hero or winning in games.

Brad Bushman, a psychology professor at the University of Michigan, said the study does not allow conclusions about which came first — Internet addiction or aggression.

It could be that using the Internet causes people to behave more aggressively or it could be that aggressive people seek out the Internet, he said. Or some other third factor could cause both people with poor social skills dont have any friends, so they spend a lot of time on the Internet and cant resolve conflicts in non-aggressive ways.