Alpha rhythm

• 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

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Alpha rhythm of 9 Hz, posterior dominant with waxing and waning