MRI brain scans showed children who spent the most hours in front of the box had greater amounts of grey matter in regions around the frontopolar cortex - the area at the front of the frontal lobe.But this increased volume was a negative thing as it was linked with lower verbal intelligence, said the authors, from Tohoku University in the city of Sendai.

‘These areas show developmental cortical thinning during development, and children with superior IQs show the most vigorous cortical thinning in this area,’ the team wrote.They highlighted the fact that unlike learning a musical instrument, for example, programmes we watch on TV ‘do not necessarily advance to a higher level, speed up or vary’.

‘When this type of increase in level of experience does not occur with increasing experience, there is less of an effect on cognitive functioning,’ they wrote.