There are 2 sides to this. On one hand people have undergone total or subtotal hemispherectomies with minimal to no changes to their cognitive function, or othe

There are 2 sides to this. On one hand people have undergone total or subtotal hemispherectomies with minimal to no changes to their cognitive function, or other personality aspects. On the other hand this doesn't imply that you can remove anything "up to" 50%. Some bits are "make or break". To make a CPU analogy, plenty of CPUs can (are designed to) function just fine with disabled cores. But certain units cannot be disabled and still have a functional CPU. The IMC or chip interconnect may take little die space but would leave the CPU dead in the water if removed. Not all parts of the brain are created equal, not 100% of the brain is there for us to "use" (as in we're not consciously using them, they provide autonomous "built-in" functions), and the parts that we consciously make use of might very well be underused. Few people would ever need to use at once all parts of the brain for all possible processing needs like all types of sensorial input processing, all types of memory memory, all types or reasoning, empathy, multitasking, etc. So they'll use a few at a time. Maybe 10%.