Social network sites risk infantilising the mid-21st century mind, leaving it characterised by short attention spans, sensationalism, inability to empathise and a shaky sense of identity, according to a leading neuroscientist.

The startling warning from Lady Greenfield, professor of synaptic pharmacology at Lincoln college, Oxford, and director of the Royal Institution, has led members of the government to admit their work on internet regulation has not extended to broader issues, such as the psychological impact on children.

Greenfield believes ministers have not yet looked at the broad cultural and psychological effect of on-screen friendships via Facebook, Bebo and Twitter.

She told the House of Lords that children's experiences on social networking sites "are devoid of cohesive narrative and long-term significance. As a consequence, the mid-21st century mind might almost be infantilised, characterised by short attention spans, sensationalism, inability to empathise and a shaky sense of identity".

Arguing that social network sites are putting attention span in jeopardy, she said: "If the young brain is exposed from the outset to a world of fast action and reaction, of instant new screen images flashing up with the press of a key, such rapid interchange might accustom the brain to operate over such timescales. Perhaps when in the real world such responses are not immediately forthcoming, we will see such behaviours and call them attention-deficit disorder.

"It might be helpful to investigate whether the near total submersion of our culture in screen technologies over the last decade might in some way be linked to the threefold increase over this period in prescriptions for methylphenidate, the drug prescribed for attention-deficit hyperactivity disorder."

She also warned against "a much more marked preference for the here-and-now, where the immediacy of an experience trumps any regard for the consequences. After all, whenever you play a computer game, you can always just play it again; everything you do is reversible. The emphasis is on the thrill of the moment, the buzz of rescuing the princess in the game. No care is given for the princess herself, for the content or for any long-term significance, because there is none. This type of activity, a disregard for consequence, can be compared with the thrill of compulsive gambling or compulsive eating.

"The sheer compulsion of reliable and almost immediate reward is being linked to similar chemical systems in the brain that may also play a part in drug addiction. So we should not underestimate the 'pleasure' of interacting with a screen when we puzzle over why it seems so appealing to young people."

Greenfield also warned there was a risk of loss of empathy as children read novels less. "Unlike the game to rescue the princess, where the goal is to feel rewarded, the aim of reading a book is, after all, to find out more about the princess herself."

She said she found it strange we are "enthusiastically embracing" the possible erosion of our identity through social networking sites, since those that use such sites can lose a sense of where they themselves "finish and the outside world begins".

She claimed that sense of identity can be eroded by "fast-paced, instant screen reactions, perhaps the next generation will define themselves by the responses of others".

Social networking sites can provide a "constant reassurance – that you are listened to, recognised, and important". Greenfield continued. This was coupled with a distancing from the stress of face-to-face, real-life conversation, which were "far more perilous … occur in real time, with no opportunity to think up clever or witty responses" and "require a sensitivity to voice tone, body language and perhaps even to pheromones, those sneaky molecules that we release and which others smell subconsciously".

She said she feared "real conversation in real time may eventually give way to these sanitised and easier screen dialogues, in much the same way as killing, skinning and butchering an animal to eat has been replaced by the convenience of packages of meat on the supermarket shelf. Perhaps future generations will recoil with similar horror at the messiness, unpredictability and immediate personal involvement of a three-dimensional, real-time interaction."

The solutions, however, lay less in regulation as in education, culture and society.

Greenfield argued that the appeal of Facebook lay in the fact that "a child confined to the home every evening may find at the keyboard the kind of freedom of interaction and communication that earlier generations took for granted in the three-dimensional world of the street. But even given a choice, screen life can still be more appealing."

She quoted one user saying they had 900 friends, another saying the fact "that you can't see or hear other people makes it easier to reveal yourself in a way that you might not be comfortable with. You become less conscious of the individuals involved [including yourself], less inhibited, less embarrassed and less concerned about how you will be evaluated."

But Greenfield warned: "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. We know that the human brain is exquisitely sensitive to the outside world."