Your brain is a constant hum of electrical activity. This activity isn't random; it's composed of rhythmic, oscillating patterns called neural oscillations, or brainwaves. We classify these waves based on their frequency, which is measured in Hertz (Hz) — the number of cycles per second.

Think of it like music. Low-frequency waves are like the slow, deep beat of a bass drum, while high-frequency waves are more like the quick, sharp notes of a piccolo. In the brain, these different rhythms correspond to different states of consciousness, from deep sleep to intense focus.

A key principle to remember is the inverse relationship between a wave's frequency and its amplitude, or power. Generally, slower waves have a higher amplitude, meaning they are more powerful and easier to detect. Faster waves tend to have a lower amplitude. This is because high-frequency activity often reflects localised, complex processing, while low-frequency rhythms like delta waves often involve large populations of neurons firing in synchrony, creating a powerful, unified signal.

Neuroscientists have identified five primary types of brainwaves. Each occupies a specific frequency band and is associated with different mental activities. From slowest to fastest, they are Delta, Theta, Alpha, Beta, and Gamma.

As you can see, the spectrum covers a wide range of mental states. When you're solving a complex problem, your brain is likely producing a lot of beta waves and gamma waves. When you're winding down for the night, alpha waves become more prominent, eventually giving way to theta and delta as you fall asleep.

Remembering the order of these waves, especially when you're just starting out, can be tricky. A common mnemonic sorts the four main wave types by speed, from fastest to slowest: B-A-T-D.

Beta (Fastest, active mind) Alpha (Relaxed, passive) Theta (Drowsy, light sleep) Delta (Deepest sleep)

Think of it as the reverse of a bat flying out at night; you start active and gradually slow down into sleep. Gamma waves, being the fastest, can be thought of as an overdrive mode beyond Beta. For a complete order from slowest to fastest, you can remember Deep Thinking Always Beats Guessing (Delta, Theta, Alpha, Beta, Gamma).

Understanding these frequency bands is the first step toward interpreting complex EEG data.