A couple of choice quotes:
"He found that just being in a situation where you are able to text and email - perhaps sitting at your desk - can knock a whole ten points from your IQ. This is similar to the head-fog caused by losing a night’s sleep."
"An American study reported in the Journal Of Experimental Psychology found that it took students far longer to solve complicated maths problems when they had to switch to other tasks - in fact, they were up to 40 per cent slower.
The same study also found multitasking has a negative physical effect, prompting the release of stress hormones and adrenaline.
This can trigger a vicious cycle, where we work hard at multi-tasking, take longer to get things done, then feel stressed, harried and compelled to multi-task more."
"Using brain-scans he’s found that if we multi-task while studying, the information goes into the striatum, a region of the brain involved in learning new skills, from where it is difficult to retrieve facts and ideas. If we are not distracted, it heads to the hippocampus, a region involved in storing and recalling information."