It was interesting to read. There aren't many google results for 'multiple demand network' that I could easily parse, but I did happen to find this paper on it in primates[0] (also happens to be from MIT) when I was trying to find an image that showed what parts of it are activated. I found this slide from a lecture very interesting[1].
[0]: http://web.mit.edu/9.s915/www/classes/duncan.pdf [1]: https://i.imgur.com/xdYzbev.png