The result is similar to a lobotomy but I what was done to him was more 'pocking around someone's brain and destroying some parts/severing some connections to see how/if they'll heal'

(the answer is that Valya is able to heal nearly everything, but the tissue that is regenerated is pretty much useless (think of it like fibrous connective tissue, vascularized but not much else), so lost connections remain lost even if his body will fill the gaps)