posterior dominant rhythm

aka PDR, alpha rhythm, posterior rhythm

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  • Present in the awake state with eyes closed; attenuates with eye opening. In other words, it is reactive to eye opening.
  • Located over the occipital regions.
  • Normally between 8 or 8.5 Hz and 12 Hz.
  • Abnormal if the maximal amplitude on one hemisphere is less than 50 percent that of the contralateral hemisphere.

clinical significance

The presence of a normal reactive posterior dominant rhythm is indicative of a well-functioning brain and automatically rules out all sorts of pathology. In a patient with altered mental status where the differential includes seizures, encephalopathy, or something psychogenic, the presence of a normal reactive PDR is a very strong argument against the first two.

related topics:

  • alpha squeek
  • fast alpha
  • slow alpha