A leading scientist at Oxford University has claimed that social networking websites are causing alarming changes in the brains of young users by making them more self-centred and cutting their attention span, the 'Daily Mail' reported.

According to Susan Greenfield, popular social networking sites such as Facebook, Twitter and Bebo are said to shorten attention spans, encourage instant gratification and make young people more self-centred.

And, repeated exposure to the sites could effectively "rewire" the brain, Greenfield said, adding that online games and fast-paced TV shows were also other factors.

"We know how small babies need constant reassurance that they exist. My fear is that these technologies are infant ilising 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 said.

Moreover, she said that exposure to computer games, instant messaging, chat rooms and social networking sites can leave a generation with poor attention spans.