Scientists, sort of at the end of the 20th century, learned that they could track blood flow to map non-invasively where activity was going on in the human brain.
科学家们在大约20世纪晚期的时候 发现他们可以通过非侵入式的方法 来追踪血液的流动 从而绘制出在人类大脑里活动进行的区域图。