They are talking about an increase only over the past 20 years. But most pollution levels have been steadily decreasing over that time in Western countries.

To answer this, one has to answer two questions:

What new influence on brain tissue has increased rapidly over the past 20 years only?

My first knee-jerk take on this when I heard the story was cell phones. While no hard data has shown up on this showing any significant harm, I would not be terribly shocked if someday some cumulative bad effect was found from low levels of electromagnetic radiation sleeting through our bodies 24/7 for the past century. Anybody remember Heinlein's story, "Waldo?" But that just brings up a much more perplexing question:

Why are Japanese, who live in a highly-industrialized society with at least as many pollutants as everywhere else, and where they have cell phones practically grafted to their ears, have a low rate of these problems? Is it the food? What food? Something they all eat in Japan and never eat overseas? Something they eat overseas that they never eat in Japan? I can't think of anything like that off the top of my head.

If it was genetic to Japanese, it wouldn't change when they moved.

I'm stumped. Anyone else?