LIBRARYWhat Is EEG & How Does It Work?

EEG (electroencephalography) records the brain's electrical activity from the scalp. What the signal actually is, what it can tell you, and what it can't.

EEG (electroencephalography) is a way to record the brain's electrical activity using electrodes placed on the scalp. When large populations of neurons fire together, the tiny voltages they produce sum up and reach the scalp as a fluctuating signal of a few microvolts. EEG measures that signal as voltage over time. It is a recording of electrical rhythm, not a picture of the brain.

What makes EEG special: timing

What makes EEG special is its timing. It captures changes millisecond by millisecond, so it's superb at telling you when something happens in the brain. The trade-off is location: because the signal is blurred crossing the skull and scalp, EEG has poor spatial resolution and can't pinpoint where deep in the brain an event came from. It is also strictly a measurement: it reads the brain's own activity and puts nothing in.

WHAT IS EEG

From firing neurons to a few microvolts

Neuron populations
fire together, in sync
Voltages sum
into one tiny field
Through skull + scalp
blurred and attenuated
At the electrode
a few µV, over time

timing: millisecondplace: blurred

Great timing, poor place. EEG reads electrical rhythm over time, not a picture of where in the brain it came from.

EEG vs fMRI, MEG, and fNIRS

Method	Strength	Trade-off
EEG	Millisecond timing, cheap, portable, non-invasive	Poor spatial resolution; noisy
fMRI	Excellent spatial detail, whole brain	Slow (seconds), huge & expensive, not portable
MEG	Good timing + better localization than EEG	Enormous, shielded-room cost
fNIRS	Portable, tolerant of movement	Slow (blood-flow based), shallow

What EEG is NOT

EEG is not mind-reading and not brain imaging. It can't recover words, images, or specific thoughts. What it can do is detect patterns (rhythms, responses to stimuli, and states like relaxed-vs-alert) reliably enough to drive a brain-computer interface. Powerful, but pattern detection, not telepathy.

References

Wolpaw, Birbaumer, McFarland, Pfurtscheller & Vaughan (2002), Brain-computer interfaces for communication and control. Clinical Neurophysiology 113:767–791.

Keep going

Start here: the full EEG BCI roadmap

What you can do with it: what is a BCI?

How the signal is captured: electrodes & the 10-20 system

Curious how the microvolt signal actually gets captured and digitized? That's the hardware story: start with the chip at the center of most DIY EEG, then build the front-end in the OTD Academy EEG front-end project.

One Thousand Drones Academy · reviewed June 2026

Coming soon

8-Channel EEG Front-End on ESP32 →

Design the analog board that reads real brainwaves: the BCI.