Alpha rhythm (posterior dominant rhythm) on EEG

Alpha rhythm · 8–13 Hz · Normal

Posterior 10 Hz rhythm that blocks when the eyes open. Watch the blink, then the attenuation. Simulated trace, longitudinal bipolar channels. Open in the interactive viewer

What it looks like

The rhythm of relaxed wakefulness with the eyes closed: 8–13 Hz, maximal over the occipital regions, waxing and waning in spindles. It attenuates when the eyes open or the patient concentrates. That reactivity matters more than the exact frequency. ^3,11

What it means at the bedside

In an awake adult, a posterior rhythm below 8 Hz is abnormal. Amplitude is often a little higher on the right; a consistent difference of more than 50% deserves a look for a structural cause or a technical one (electrode spacing, skull defect). ¹¹

NormalPosteriorReactive

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Sources

Kane N, et al. A revised glossary of terms most commonly used by clinical electroencephalographers and updated proposal for the report format of the EEG findings (IFCN, 2017). Clin Neurophysiol Pract 2017;2:170–185. doi.org/10.1016/j.cnp.2017.07.002
Britton JW, et al. Electroencephalography (EEG): An Introductory Text and Atlas of Normal and Abnormal Findings in Adults, Children, and Infants. American Epilepsy Society, 2016 (free, NCBI Bookshelf). www.ncbi.nlm.nih.gov/books/NBK390354/

Alpha rhythm (posterior dominant rhythm) on EEG

What it looks like

What it means at the bedside

Sources

Related patterns