There was a time, not long ago, when people studying brains gained access to new and incredibly powerful instruments to measure what parts of the brain were more active than others. They could measure many many different places, so many that they could even sometimes tell what emotions a person was feeling just by looking at their readings!
This rush of data made researchers heady. They kept looking for more and more interesting details about how brains worked. They would look at the data lots of different ways, starting from the raw activity data. This raw data about brain activity was especially exciting — there were little sparks of activity everywhere! Most researchers were cautious, though, and only considered activity convincingly demonstrated if they first took into account that they were looking at lots and lots of measurements all at once.