Susan Greenfield, the eminent neuroscientist and head of the Royal Institution, is the latest to weigh into the debate, warning that young people's brains may be fundamentally altered by internet activity.

While concerns about children and computers have usually focused on their forging inappropriate relationships online, or failing to get enough exercise as a result of being glued to a screen, the baroness suggested the consequences may be more profound.

She told peers in the House of Lords it would be worth considering whether the rise in autism - a condition marked by difficulties forming attachments - was linked to the increasing prevalence of screen relationships.

Real-life conversations "require a sensitivity to voice tone, body language and perhaps even to pheromones - those sneaky molecules that we release and which others smell subconsciously.

"Moreover, according to the context and, indeed, the person with whom we are conversing, our own delivery will need to adapt. None of these skills are required when chatting on a social networking site," she said.

"It is hard to see how living this way on a daily basis will not result in brains, or rather minds, different from those of previous generations."

She also suggested that increasing diagnoses of Attention Deficit Hyperactivity Disorder - ADHD - may be connected to the "near total submersion of our culture in screen technologies".

Last week, a report published in the journal Biologist, suggested that a lack of face-to-face contact could alter the way genes work, upset immune responses, hormone levels and the function of arteries.

This, said author Aric Sigman, could increase the risk of health problems as serious as cancer, strokes, heart disease and dementia.

Indisputably, people are spending more time online and social networking sites are increasingly popular - the BBC even has a "my CBeebies" where youngsters can create their own avatar.

Alone and ill

A number of studies have looked at the negative effects of social isolation on health: from an increased risk of cardiovascular disease to outright death, being lonely does not appear to be good for you.

But whether computers - and social networking in particular - improve or exacerbate social isolation in the first place is a moot point.

A spokeswoman for Cancer Research UK noted that there was no evidence to link the disease with using Facebook.

If anything, it has been suggested, social networking may improve the quality of life of those with cancer by allowing those affected to make contact.

Baroness Greenfield meanwhile points out that those on the autism spectrum are particularly comfortable in the cyber world.

"She's right about that, but her analysis is the wrong way round," said Professor David Skuse, of the Behavioural Sciences Unit at the Institute of Child Health.

"The young people with autism we see do have a problem with face-to-face communication although they can be very articulate. They need to communicate and the internet is giving them a channel that they would not otherwise have.

He added: "As for ADHD, it's true that I have yet to meet a child who could not concentrate on a computer. It seems to give them a way to focus in a way that lessons at school do not. Most of those with ADHD find their condition very distressing and want a way to control it - they want a way to focus."

In and out

Nonetheless Baroness Greenfield's overriding concerns about an ever more self-absorbed generation unable to empathise with others do chime with popular fears, says Helene Guldberg, a psychologist and author of Reclaiming Childhood: Freedom and Play in an Age of Fear.

"Technology is something of an easy target when perhaps we should be asking more difficult questions about our relationships with our children.

"But it is true that in an ideal world children would be freer to pursue their friendships and activities outdoors, on the street, away from the watchful and worried eyes of their parents.