Mobile Use and the Brain

I was fascinated by this article on mobile phone use and its impact on the brain, from the BBC website.
Apparently using a mobile phone affects the brain's consumption of blood sugar. But a scientist also remarked "Much larger fluctuations in brain metabolic rate occur naturally, for example during thinking."
The implication seems to be that the act of thinking is completely different to using mobile phones. Which, I suppose, explains some of the conversations I hear on trains.