Alpha rhythm

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  • Frequency: 8-13 Hz
  • Posterior dominant
  • Amplitude: 10-80 microV
  • Wax and wane in amplitude
  • Most prominent with eyes closed and relaxed
  • Suppressed with eyes open, mental stress or sleep
  • Left-right difference <1 Hz in frequency and <50% in amplitude (amplitude is usually higher on the right side)
  • Alpha variants are normal sub- and supraharmonic frequencies of the alpha rhythm, particularly in children and young adults.
  • The posterior basic rhythm frequency is age dependant:
    • 0-3 months: No posterior basic rhythm
    • 4 months: 3-4 Hz
    • 5 months: 5 Hz
    • 1 years: 6-7 Hz
    • 3 years: 8 Hz
    • 7 years: 9 Hz
    • > 60 years: Decrease by 0.08 Hz/year
Alpha rhythm