One topic in neuroscience that gets a lot of attention in recent years is the "mirror neuron" thing (see here, here, or here). Decades ago, Rizzolatti et al. discovered that certain neurons would fire whether the subject was performing a relevant task or just watching someone else perform the same task.
Lots of fun discussion exists on the meaning of this.
My quick take is that it at least suggests modularity in the brain. If I developed a well-factored software API for handling any task of any sort (really, speaking of any half-serious software here), I would build reusable functions to support various aspects of the system. That's just expected, right?
Well, say I have some code paths using helper functions that actually do visible IO (say to a database or a web page or a robot arm or ...), the same helper functions would also likely get used in other contexts.
Drop a trace of some sort in said helper function, and you'd see it being used whether for visibly active things or not.
Mechanics and various use cases aside, that seems clear to me what is happening in mirror neurons. Much of the research exists around "what specific use case would these reusable functions have" and that's definitely interesting, but to me, the core is that reusable modularity is going on.
In a bit more searching, I also just learned that relevant term sometimes used in neuroscience is subserve (or subserving).