So, is it possible to dump nonessential cortical functions and repurpose the relevant brain sectors for extra cognitive ability?
Would you achieve a 1:1 performance gain from the recruited brain sectors or would there be some inefficiency due to them being specialised for a task other than what they're being used for?
Brain regions are not just generic cpus you can arbitrarily subdivide and repurpose for other tasks, many are quite specialized in their arrangement and have a limited spectrum of usefulness. Some can learn to perform different functions over time, some cannot.
You also have to consider what is connected to what, the layout of white matter tracts, how this relates to the whole, etc. Look into pyramidal cells is you want a starting point to see what I mean.
Yeah that's why I mentioned a performance drop from cross purpose use.
For instance I read a paper about training mice to 'see' the feed of a camera through the sensory cortex, but they learned much faster when the electrodes were attached on the visual cortex.