What does it mean when an EEG shows strong alpha or strong delta? · Grey Matter

An EEG is usually read by splitting it into bands: delta below about 4 Hz, theta about 4 to 7 Hz, alpha about 8 to 12 Hz, beta about 13 to 30 Hz and gamma above about 30 Hz, with edges that vary slightly between textbooks.

What does it mean when an EEG shows strong alpha or strong delta?

An EEG is usually read by splitting it into bands: delta below about 4 Hz, theta about 4 to 7 Hz, alpha about 8 to 12 Hz, beta about 13 to 30 Hz and gamma above about 30 Hz, with edges that vary slightly between textbooks. Strong alpha over the back of the head is the normal pattern of an awake person at rest with the eyes closed, and it shrinks when the eyes open. Strong delta is normal in deep sleep and abnormal in an awake adult, where it can point to a damaged or depressed patch of cortex. A band's power says how many neurons are oscillating together at that pace, so it describes the state of the tissue rather than any specific thought.