The Extended Mind is an ambitious book, one which tries to link together a lot of science and social science research into many subjects. Part of the discussion is the way in which our body affects our mind and brain; if we sense, gesture, or move it impacts the working of our brains in specific areas and ways. Space also impacts: are we in natural surroundings or built ones, can we use space to extend our memory (the "memory palace" method). Finally how do groups (experts, peers, diverse groups) affect us. The thrust of the discussion is how we can use the information/research to improve our thinking and effectiveness.
I found myself skimming. One of the Amazon reviews complains about the author's narration in the audible book being monotonal; there's something of a monotone about her writing as well (it would have been improved by following her own advice--adding graphics to the book, particularly for the "conclusions"). It would have been more useful if I were younger. I did skim all the way through, and actually I found the last chapter ("thinking with groups") the most interesting, likely not in the way she intended.
As I read, two phenomena came to mind: the death of the concertgoers in Houston and Trump's rallies. She writes about how groups, particularly students or coworkers, can be more effective, but some factors are common: a common focus (speaker, performer) and common engagement. Both were likely present in Houston and in Trump's rallies. I suspect I'm not too different from many liberals in dismissing the rallies in the past. But after reading the chapter I'm reconsidering, particularly in the light of Houston. Just because I'm proudly individualistic (I write with tongue in cheek) doesn't mean that others are.