neural oscillation (brainwave)

A neural oscillation is a rhythmic rise and fall of activity shared across a large group of neurons firing roughly in step. Like a stadium crowd clapping together, the synchronized beat is far easier to detect than any single hand. These rhythms are exactly the "brainwaves" an EEG picks up from the scalp.

Oscillations are sorted by speed into named frequency bands — delta, theta, alpha, beta, gamma, from slowest to fastest. Different bands tend to dominate in different states: slow delta waves swell in deep sleep, while faster rhythms accompany alert, focused thinking. So the mix of rhythms is a rough readout of what the brain is doing.

This makes oscillations a favorite signal for BCIs, especially non-invasive ones. Rather than chase individual spikes it cannot see, a scalp BCI watches how the strength of a particular rhythm rises or falls as you change what you are doing or imagining.