Which of the following represents an abnormal EEG pattern?

• A. Well formed posterior dominant rhythm of 17Hz
• B. Alpha voltage of 20uV in O1 and 28uV in O2
• C. Alpha frequency of 9Hz in O1 and 11.5Hz in O2
• D. Alpha squeak

Answer: (D)

The presence of an alpha squeak on an EEG can be indicative of an abnormal pattern. An alpha squeak is characterized by a brief and sudden increase in alpha activity, which can reflect atypical brain function. It often serves as a marker for conditions such as sleep disorders or epileptic disturbances, thereby distinguishing it from typical, well-formed alpha activity that is expected during relaxed but awake states.

The other options reflect normal EEG characteristics. A well-formed posterior dominant rhythm of 17Hz is part of the expected range for awake adults and signifies healthy cortical activity. Alpha voltage values in the range of 20μV and 28μV in the respective regions are also considered normal and suggest properly functioning cortical structures. Lastly, while alpha frequencies typically range from 8 to 13Hz, having frequencies of 9Hz and 11.5Hz in O1 and O2 regions can still be interpreted as within the normal variability for alpha rhythm.

This understanding of what constitutes normal versus abnormal patterns is critical for electroencephalographic assessment, particularly in the identification of possible neurological conditions.