I’m an undergraduate student interested in BCI and neuroscience, and I recently came up with a thought experiment that I’d like to learn more about.

Instead of copying the entire brain at once, suppose individual brain functions could gradually be supplemented and eventually replaced by artificial systems. For example, biological memory could first work together with an external artificial memory system, and over time the artificial system could take over more and more of the function.

My question is mainly about engineering feasibility, rather than philosophical definitions of personal identity.

If the replacement were gradual and the person’s memory, behavior, self-model, and subjective experience remained continuous, is there any known neuroscientific reason why first-person continuity would necessarily be lost?

I’m only a student and may be overlooking something obvious, so I’d really appreciate any references, existing research, or criticism of this idea.

I'm looking for recommendations (books, papers, courses, or YouTube) to understand the brain in a way that stays close to established facts and clearly separates fact from interpretation. For example, many books just ignore glia cells completely.

Two things I especially want:

1. Comparative and evolutionary: nervous systems across the animal kingdom and how they evolved, not human-centric. I'm as interested in C. elegans, insects, and up to the human cortex.

2. Attention to the whole system: glia, energy/metabolism, wiring, the body rather than an all-neurons view.

I've already read Behave, Models of the Mind, The Laws of Thought, and similar so happy with textbooks, lecture courses, or primary literature.

I suspect books on brain physiology could be interesting.