How does re-sleeving work?

Question

One of the main, (if not the main) plot mechanics in Altered Carbon is that the consciousness/memories of people can recorded by the cortical stacks installed in the cervical part of their spines. This facilitates transferring of a person's consciousness to a new sleeve.

But how does the re-sleeving process work? If the stack simply records a person's "state" then the sleeve's biological brain is still performing all the actions (like moving/thinking/remembering etc.). So that when you insert a stack into a pre-owned sleeve, the consciousness it contains should be at odds with the sleeve's existing biological consciousness.

Or does the re-sleeving process imply some sort of mind-wipe/mind-overlay/mind-reboot of the sleeve's brain?

Alternatively, if the stack is doing the driving - what is left for the higher functions of the sleeve's brain to do?

Answer 1

In Altered carbon, the human bodies are referred to as "Sleeves" and the process of transferring one's consciousness to another body is called "re-sleeving" (as you clearly mentioned).

According to the Alter Carbon wikia site (here):

The mind is no longer fixed to the body, because the stack contains the human mind. The mind (the DHF) can be transferred via “needlecasting” to any other stack in any other sleeve, provided that the stack is wiped before the transfer.

The sleeve you are born into is called your “birth sleeve.”

When a sleeve dies, but the stack is still intact, this is called “sleeve death.” It is not fatal to the mind, only the body.

So, the stack simply doesn't record human actions, IT LITERALLY RECORDS EVERYTHING. Then the re-sleeving is done by first wiping the sleeve's stack and then transferring the consciousness from the person's stack into the sleeve's stack.

But on the downside,

The human mind is biologically evolved to stay within the body into which it was born. If a person is resleeved too many times, the mind will rebel, and the personality starts to fragment. In short, resleeve into too many different bodies, too many times, and you go insane.

If a person resleeves into their own biological body over and over, however, there is no personality frag.

This is why Meths grow clones to resleeve into; they can live forever without any personality degradation or fragmentation.

And finally about "what is left for the higher functions of the sleeve's brain to do?". According to the book:

Cortical stacks serve as a receptacle for the human consciousness or Digital Human Freight (DHF).

In simple terms, they are like recorders; they take note of everything that happens. But still the brain of the sleeve is responsible for the sleeve's functionality. Take for example the action of thinking. The brain thinks, but the sleeve 'records' what the brain thinks. And all higher order functionalities are done by the brain. This is why rich people (who cannot afford clone re-sleeving) buy the sleeves that have great skills (like the one Bancroft acquired for Kovachs).

Answer 2

Neither the book or the tv show go in the detail of how the "stack" and brain work. Instead, I believe the IT analogy is used:

The human brain is hardware, the mind is the software and the stack is the backup system for the mind. When the brain dies (because the sleeve has died), the stack can be used to copy the last existing state of the mind (i.e. people remember how they've died) and imprint it on a new brain in a new sleeve. In a similar fashion, a consciousness from a stack can be uploaded into a virtual reality where it can inhabit a virtual (although feeling to the mind like a real) body.

The details of the process are not described in details but we know that the sleeve has also an impact on the mind, for example, the new user can inherit some habits of the old sleeve - in the book, Kovacs feels the urge to smoke because the original owner of his sleeve was a smoker; he also is very attracted to Detective Ortega, because the original owner was in love with her. However, the higher functions of the new sleeve are gone, there is no old "consciousness" within it - for all purposes, the un-stacked sleeve is brain dead.

As mentioned in @Shreedhar answer there is a need for basic compatibility before resleeving and uploading stack to incompatible sleeve (although it is not really described what "compatibility" means as uploading child to the adult body or a woman to men's one has been done successfully) can lead to severe mental trauma. Sometimes this is done on purpose as a way to torture - for example by uploading people into wild animal bodies and sending them to fight in arena.