4. 1 and 3
Frontal intermittent rhythmic delta activity (FIRDA) was originally described by Cobb in 1945 (4). FIRDA is a rhythmic 2 to 3 Hz delta frequency activity with an amplitude of 50–100 mv that predominates in the bilateral frontal regions of the adult electroencephalogram (EEG) (5). The waves are usually regular with a sinusoidal pattern. FIRDA usually occurs in short bursts lasting 2 to 6 seconds and must be differentiated from slow eye blink artifact. The electrooculogram (EOG) electrodes can aid in the differentiation of the two. FIRDA, unlike eye blink artifact, may have posterior field extension. It is attenuated by alerting or eye opening and accentuated by eye closure, hyperventilation, drowsiness, and stage N1 sleep. It disappears with the onset of Stage N2 sleep but may reappear during REM sleep. In our patient, alerting and eye opening did not reproduce the EEG pattern. No history of seizure activity was obtained and no seizures were observed during the polysomnography while the EEG was being recorded.
What are potential causes of FIRDA? (Click on the correct answer to proceed to the fifth of six pages)