When a patient with brain disease visits a doctor, he or she may tell the patient, “You have a tumor in a functional area, and you may have dysfunction after surgery”. So, what is a functional area? The brain has many subdivisions. The so-called functional areas are those related to limb movement, sensation, speech and vision. For example, the precentral gyrus is related to limb movement, the postcentral gyrus is related to sensation, the posterior left superior temporal gyrus, the posterior left inferior frontal gyrus, and the left angular gyrus are related to language activity, and the medial occipital lobe is related to vision. Lesions in these areas impair the corresponding functions and manifest as hemiplegia, aphasia, and hemianopia.