In EEG terminology, what does a "spike" signify?

A "spike" in EEG terminology signifies a sudden increase in voltage that indicates abnormal activity in the brain. Spikes are brief, sharp waves typically lasting less than 70 milliseconds and arise from a focal region of the brain. They are often associated with various forms of epilepsy and other forms of abnormal electrical activity.

In contrast, the other answers describe different EEG phenomena. For instance, a consistent pattern of brain activity does not necessarily connect with spikes, as spikes are infrequent transient events rather than consistent patterns. Slow waves associated with deep sleep refer to another category of brain activity, specifically delta waves, which indicate a state of restful sleep rather than abnormal activity. General electrical noise refers to non-specific disturbances in the signal that do not reflect recognizable brain function and are different from the defined and specific nature of spikes. Thus, understanding spikes as indicators of sudden and abnormal electrical discharges is pivotal in EEG interpretation.