Generate a topic word for the given sentence. A topic word is usually the name of a person, place, animal, concept or object the sentence is focusing on.

[Q]: the occipital lobe is the back part of a mammal's brain.
[A]: occipital lobe


[Q]: tactopods are members of a proposed clade of ecdysozoans called tactopoda.
[A]: tactopoda


[Q]: a stimulus (plural stimuli) is something which causes a response.
[A]:
stimulus