eloquent

1. (medicine) Relating to areas in the brain that serve an identifiable neurological function, in which injury leads to focal deficits or disability.Examples: "Lydiard was diagnosed shortly after new year following speech disturbance and subtle memory issues. He has a high-grade glioma, an aggressive malignant primary brain tumour in the left side. It is in the “eloquent brain”, very close to the part that controls speech, and would have been considered untreatable in the past."