EEG results for dementia patients. Can anyone share insights?

My mother had an EEG a year ago. She was cooperative with the entire process. The results were normal.

After the discovery of EEG by Berger in 1924, it has been used primarily in the diagnosis and management of seizure disorders. With more sensitive equipment, it can be of help in diagnosing encephalopathies, brain lesions, brain infections, brain tumors, stroke, dementia and other structural brain pathologies. However, it has many limitations. The placement of the electrodes in the scalp can only pick up electrical signals produced in the superficial layers of the cerebral cortex. Lesions that are too deep in the brain will not send electric signals far enough to reach the scalp. Even in the diagnosis of epilepsy, there is about 35% of cases in which the recording is "normal". In well established dementias, the EEG does show electrical abnormalities, but it could be normal in the early stages. However, EEG is being investigated as potential non-invasive tool to detect very early signs of Alzheimer's. Also to follow up the progression of the dementias. Currently is of limited value. There is another limitation. It requires a lot of cooperation from the patient. The brain waves change if the patient keeps the eyes open, closed or if he is blinking. Same, if the brain is at rest, relaxed, tense, anxious, attentive, drowsy or asleep. A patient with dementia might not be able to follow complex directions.