Biomedical Engineer Question:

Electroencephalography is commonly known as EEG. It is the recording of the electrical activity along the scalp. This technique can measure the fluctuations in voltage resulting through the ionic flow of current within the neurons of the brain. In EEG multiple electrodes are placed on the scalp which is used to record brain's spontaneous electrical activity over a short period of time. EEG can be used for the diagnosis of coma, encephalopathies, and brain death.
Wave patterns commonly observed in EEG are delta - state of sleep, theta - drowsiness, alpha - relaxation, and beta - active thinking and gamma.