Which of the following represents an abnormal EEG pattern?

An abnormal EEG pattern is indicated by interictal spikes, which are sharp waves or spikes seen on the EEG during periods of no seizure activity. These spikes are typically associated with certain neurological conditions, including epilepsy. The presence of interictal spikes signifies underlying cerebral dysfunction.

In contrast, while alpha frequency of 9 Hz in O1 and 11.5 Hz in O2 shows a variance in the alpha rhythm across different regions, it does not necessarily define an abnormal pattern on its own. Alpha rhythms typically range from 8 to 12 Hz, and although slight discrepancies in frequency can reflect differing states of alertness or attention, interictal spikes are a more definitive indicator of abnormality.

Theta rhythm can be abnormal or normal depending on the context, but in many cases, particularly in adult patients while awake, it can signify some form of cerebral dysfunction when appearing in specific locations or without an appropriate context. Normal alpha activity is, of course, entirely standard and not considered abnormal.

Thus, interictal spikes are clearly recognized as abnormal findings in EEG analysis, as they specifically point to neural disturbances that warrant further investigation.