Scott Fraser and his colleagues study the zebra fish’s pallium because it resembles the human amygdala, the centre in the brain where emotions like fear and anger are regulated. The pallium is easier to study than the amygdala because it is more easily accessible: while the amygdala is hidden deep inside the brains, the pallium is on the surface because the zebra fish sort of pops its brains inside out like a popcorn kernel. In addition, young zebra fish are transparent, so that makes it easier to look inside the fish without having to cut it open.