Home > Conscious > Chapter 4 > 4.3. Brain Waves


Brain waves are the result of synchronous oscillations by a large population of neurons, the more neurons fire simultaneously, the greater the amplitude of brain waves (Figure 4-9). For voltage fluctuations on the scalp to be detected, it is estimated that more than ten thousand neurons are required to fire synchronously.


Figure 4-9. The relationship between EEG or MEG results and the firing of single neurons. The more neurons fire simultaneously, the greater the amplitude. [Source: Adjamian, 2014 ]

Based on frequency, brain waves are divided into several types, denoted by Greek letters. Each plays distinct roles.

  • Alpha (α) waves: 8-12 Hz, the dominant brain wave while awake, crucial for attention.
  • Beta (β) waves: 16-25 Hz, responsible for the timing of movement.
  • Gamma (γ) waves: > 30 Hz, encoding memory and external signals.
  • Theta (θ) waves: 4-7 Hz, working with γ waves for the processing of memory and external information.
  • Delta (δ) waves: 1-4 Hz, most obvious during sleep.

The frequency structure of brain waves is very intriguing. The median values for α, β and θ waves are about 10 Hz, 20 Hz and 5 Hz, respectively. That is, θ frequency is about half of α frequency, while β frequency is about twice of α frequency. Such frequency structure is not accidental, but may play important roles in cross-frequency coupling (Klimesch, 2012). For example, if α and θ waves oscillate at their median values, 10 Hz and 5Hz, respectively and they are in phase, then every two α cycles, both will reach their oscillation peaks simultaneously. In this case, α and θ waves will have the best synchronization, enabling the information carried by θ-γ oscillations to enter the conscious system created by α oscillations (Chapter 8). On the other hand, suppose θ is at 5 Hz while α deviates from 10 Hz, their coupling would be weaken. The conscious system seems to use this principle to select the desired information for attention. Further details will be discussed in later chapters.