Electroencephalography
Also known as: EEG
A technique that measures electrical activity from the brain through electrodes on the scalp. Provides millisecond-level temporal resolution.
Electroencephalography (EEG) records the electrical activity of the brain from electrodes placed on the scalp. It is the oldest non-invasive technique for measuring brain activity, dating back to the 1920s, and remains essential in both clinical neurology and cognitive research.
Unlike functional MRI, which captures slow blood-flow changes, EEG captures the brain's electrical signals directly, with millisecond precision.
How it works
When large populations of neurons fire in synchrony, they produce small voltage fluctuations that travel through the skull to the scalp. Electrodes pick these up. The result is a continuous time-series of voltage values, one trace per electrode.
A standard clinical EEG uses 19 to 32 channels. Research and high-density setups can use 64, 128, or 256.
What it measures
EEG signals are typically analysed in several ways:
- Frequency bands: delta, theta, alpha, beta, gamma. Different bands correspond to different brain states. Alpha increases when eyes close, beta when concentrating, gamma during active processing.
- Event-related potentials (ERPs): time-locked responses to a specific stimulus, like the well-known P300 wave that appears around 300 ms after an unexpected event.
- Functional connectivity: how synchronised activity is between different regions.
- Microstates: brief stable patterns of whole-brain activity that switch every 80 to 120 ms.
Strengths and limits
- Strength: excellent temporal resolution, portable, relatively inexpensive, well tolerated
- Limit: poor spatial resolution. The skull and scalp blur the signal. Estimating where activity originated is an active research problem.
In clinical use
EEG is the standard tool for diagnosing epilepsy and characterising sleep stages, as well as for monitoring brain function during surgery and in intensive care.
At Neureka
We are extending our analytical pipelines from MRI to EEG. If you are working on a study where EEG analytics would help, that is a conversation we would like to have early. See our services page.
Related terms
Functional MRI
An MRI technique that maps brain activity by detecting changes in blood oxygenation as different brain regions work harder or rest.
MRI
A non-invasive imaging technique that uses strong magnetic fields and radio waves to produce detailed images of the brain's soft tissue structure.
Default mode network
A set of brain regions that are most active when the mind is at rest and not focused on an external task — linked to self-referential thinking, memory retrieval, and mind-wandering.