EEG stands for electroencephalogram
It’s a test that records the electrical activity of your brain.
Your brain is always active — even when you’re asleep — and its cells (called neurons) send tiny electrical signals to each other all the time. An EEG picks up those signals using small sensors (called electrodes) that are placed gently on your scalp.
When the test is running, those signals are shown as wavy lines on a computer screen.
Doctors or researchers can look at the waves to understand how the brain is working — for example, to study sleep, attention, or seizures (like epilepsy).
It doesn’t hurt at all — it’s safe, painless, and noninvasive — and it’s been used for decades to help understand how the brain behaves in different situations.
Your brain’s neurons communicate using tiny bursts of electricity. When groups of neurons fire together in patterns, they create brain waves — rhythms of electrical activity that change depending on what you’re doing or feeling (like being awake, asleep, relaxed, or focused).
An EEG measures these brain waves.
Different brain states — or brain problems — can create distinct patterns in those waves.
For example:
Epilepsy or seizures: During a seizure, neurons fire in a sudden, strong burst. EEG can clearly pick up those bursts and show unusual “spikes” or “sharp waves.”
Sleep disorders: Different sleep stages (like deep sleep or dreaming) have unique wave patterns. EEG helps show whether someone is cycling through those stages normally.
Brain injury or coma: EEG can reveal if the brain’s overall activity is slowed, irregular, or very low — which gives doctors clues about brain function or recovery.
Mental health and cognition: In research, EEG is used to study attention, stress, or emotional processing, since these affect brain wave rhythms too.