Electroencephalography (EEG) measures electrical activity in the brain, represented by specific patterns known as brain waves. These waves are classified based on their frequency, amplitude, and function. Below is a detailed explanation of the four primary types of EEG waves: delta, theta, alpha, and beta waves.

1. Delta Waves (δ)

Key Characteristics:

  • Frequency: 0.5–4 Hz (low frequency).
  • Amplitude: High amplitude.
  • Location: Prominent in the frontal regions during sleep in adults and posterior regions in infants.

Functions:

Delta waves are most commonly associated with deep sleep (slow-wave sleep) and restorative processes. They play a crucial role in brain recovery and memory consolidation.

Clinical Significance:

- Excessive delta waves in awake adults may indicate brain injury or dysfunction.
- Prominent in conditions like encephalopathy, head trauma, or certain tumors.

2. Theta Waves (θ)

Key Characteristics:

  • Frequency: 4–8 Hz.
  • Amplitude: Variable amplitude.
  • Location: Found in the temporal and parietal regions during drowsiness or early stages of sleep.

Functions:

Theta waves are linked to relaxation, creativity, and the transition between wakefulness and sleep. They are common during light sleep and meditation.

Clinical Significance:

- Abnormal theta activity is observed in disorders such as ADHD and some forms of epilepsy.
- Excessive theta waves in awake adults may suggest focal brain pathology.

3. Alpha Waves (α)

Key Characteristics:

  • Frequency: 8–13 Hz.
  • Amplitude: Moderate amplitude.
  • Location: Predominantly seen in the occipital region when the eyes are closed and the individual is relaxed.

Functions:

Alpha waves represent a relaxed, awake state and are most prominent during calm, restful periods with closed eyes.

Clinical Significance:

- A decrease in alpha activity may occur in stress or anxiety.
- Alpha asymmetry can sometimes indicate mood disorders.

4. Beta Waves (β)

Key Characteristics:

  • Frequency: 13–30 Hz (higher frequency).
  • Amplitude: Low amplitude.
  • Location: Commonly recorded in the frontal and central regions during active thinking and alertness.

Functions:

Beta waves are associated with active mental engagement, problem-solving, and focused attention. They reflect higher cognitive processes.

Clinical Significance:

- Excessive beta activity may be linked to anxiety or hyperactivity.
- Decreased beta activity can indicate drowsiness or sedation.

Conclusion

The four primary EEG waves—delta, theta, alpha, and beta—offer valuable insights into brain function and neurological health. Their patterns vary with states of wakefulness, relaxation, and sleep, and they can also indicate pathological conditions when abnormal.