posterior dominant rhythm
aka PDR, alpha rhythm, posterior rhythm
- 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.
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.
- alpha squeek
- fast alpha
- slow alpha