An electroencephalogram or EEG is a test that measures brain activity. EEG equipment can detect abnormalities in the brain and help physicians diagnose issues such as brain tumors, brain damage due to trauma, strokes, sleep disorders, and other brain-related conditions. An EEG machine uses electrodes attached to the scalp to measure electrical impulses in the brain. The brain frequencies of each patient get printed out on paper or rendered on a computer screen. Brain specialists can look at these reports and make a diagnosis or recommend further tests.