How large was mankind’s sense of obligation? The caveman first had this feeling for his mate, then for his family. It grew until men fought and died … - Harry Harrison

We must be as stealthy as rats in the wainscoting of their society. It was easier in the old days, of course, and society had more rats when the rules were looser, just as old wooden buildings have more rats than concrete buildings. But there are rats in the building now as well. Now that society is all ferrocrete and stainless steel there are fewer gaps in the joints. It takes a very smart rat indeed to find these openings. Only a stainless steel rat can be at home in this environment.

With a mental effort, he grabbed hold of his thoughts and braked them to a stop. There was something new here, factors he hadn't counted on. He kept reassuring himself there was an explanation for everything, once you had your facts straight.

Without being too clinical, let’s say his brain was affected.