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 (Slow alpha variant and Fast alpha variant)
  • 2-5% of healthy people does not have a detectable alpha rhythm

  • The posterior basic rhythm frequency is age dependent:
Age Frequency
0-3 months No posterior basic rhythm
4 months 3-4 Hz
5 months 5 Hz
1 year 6-7 Hz
3 years 8 Hz
7 years 9 Hz
> 60 years Decrease by 0.08 Hz/year

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

Alpha rhythm average e.png