Quote Originally Posted by Paulbot View Post
Remember Rossum's trinity. Enough damage to either the spark or brain (or cog) will kill a Transformer.

I think the spark downloads (or backs up) the brain when it's removed from the body, such as the transfers. Except for the odd mutant spark (ghost) like Starscream, a disembodied spark can't really act on its own. Even the birth of a Transformer (spark into robot, forged or constructed cold) apparently needs manual intervention. So a spark with no brain keeps the essence of a TF but isn't conscious. (I think that's partly how the Garrus jail worked). When the spark is placed back in the body or in a new TF body the memories download. Manual manipulation of the brain could still leave permament personality changes that are copied across.

The brain module is their mind, memories, personality etc. Their spark is the crucial part that makes them more than a machine. It's their irreplaceable core to their being.
Your theory also makes a whole lot of sense when it comes to the G1 Headmaster process (which I guess can be applied to IDW too).

If the head is removed, the spark will choose to 'upload' to the human/nebulan component instead of the brain module causing the 'meld' of personality we see as the end result.