Boffins with too much time on their hands have come up with the startling conclusion that while Facebook boosts your IQ, Twitter turns you into a gibbering idiot.

Dr Tracy Alloway said that using Facebook worked in the same way as playing video war games and solving Sudoku however micro-blogging on ''Twitter'' and watching YouTube were all likely to weaken ''working memory''. She said that working memory involves the ability both to remember information and to use it. At a job interview, a candidate will employ working memory to match answers to questions in the most impressive way.

Dr Alloway who has a day job at the University of Stirling in Scotland, has extensively studied working memory and believes it to be far more important to success and happiness than IQ. Her team has developed a working memory training programme that greatly increased the performance of slow-learning children aged 11 to 14 at a school in Durham. After eight weeks of ''JungleMemory'' training, the children saw 10 point improvements in IQ, literacy and numeracy tests.

A number who started off close to the bottom of the class ended up near the top. She said that video games that involve planning and strategy, such as those from the Total War series, may also train working memory, Dr Alloway believes. Of course they are not that great for socialisation skills but they make you use your working memory,'' she said.

Sudoku also stretched the working memory, as did keeping up with friends on Facebook, she said. But the ''instant'' nature of texting, Twitter and YouTube was not healthy for working memory.

"On Twitter you receive an endless stream of information, but it's also very succinct and does not need to be processed. This reduces your attention span is being reduced and you're not engaging your brain and improving nerve connections."

She thinks this is behind Attention Deficit Hyperactivity Disorder (ADHD) and pointed out hat  extensive texting was associated with lower IQ scores.