Question

Normal EEG frequency range is

• A. \( \text{50-500 Hz} \)
• B. \( \text{0.5-50 Hz} \)
• C. \( \text{0.05-5 Hz} \)
• D. \( \text{1-200 Hz} \)

Hint:

Remembering the approximate frequency ranges for different EEG rhythms (Delta, Theta, Alpha, Beta, Gamma) is crucial for interpreting EEG recordings. These bands correlate with different states of consciousness and brain activity, making EEG a valuable tool in neurology and sleep studies.

Answer 1

The Correct Option is B

To solve this problem, let's examine the normal frequency range of EEG signals and analyze each of the given options.

1. What is EEG?

Electroencephalography (EEG) is a non-invasive method to record electrical activity of the brain using electrodes placed on the scalp. The recorded signals represent the summed postsynaptic potentials from pyramidal neurons in the cerebral cortex.

2. Understanding EEG Frequency Bands

EEG signals are classified into several characteristic frequency bands:

• Delta (δ): 0.5-4 Hz (slow waves, seen in deep sleep)
• Theta (θ): 4-8 Hz (drowsiness, meditation)
• Alpha (α): 8-13 Hz (relaxed wakefulness with eyes closed)
• Beta (β): 13-30 Hz (active thinking, concentration)
• Gamma (γ): 30-50 Hz (higher cognitive functions)

3. Normal EEG Frequency Range

The complete range of clinically relevant EEG activity spans:

• Lower limit: Approximately 0.5 Hz (slowest delta waves)
• Upper limit: Typically 50 Hz (fast gamma activity)
• Some research may consider up to 70 Hz, but standard clinical EEG focuses on 0.5-50 Hz

4. Analysis of the Options

- 50-500 Hz: Incorrect - misses all clinically important slow waves and includes non-physiological high frequencies
- 0.5-50 Hz: Correct - covers all standard EEG frequency bands
- 0.05-5 Hz: Incorrect - misses important alpha, beta and gamma activity
- 1-200 Hz: Incorrect - includes non-physiological high frequencies while cutting off some delta waves

5. Technical Considerations

EEG recording equipment is typically set with:

• High-pass filter: 0.5-1 Hz (to remove DC drift)
• Low-pass filter: 50-70 Hz (to eliminate muscle artifact and noise)
• Sampling rate: At least 200 Hz (to properly capture all frequencies)

6. Why This Range Matters

The 0.5-50 Hz range is clinically significant because:

• It contains all diagnostically relevant brain wave patterns
• Higher frequencies are typically muscle artifacts, not brain activity
• Lower frequencies may represent movement artifacts or equipment drift

7. Final Answer:

The normal EEG frequency range is 0.5-50 Hz, as this encompasses all clinically relevant brain wave patterns from delta to gamma waves.