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November 17, 2023
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EEG Terminology and Waveforms (

Yamada, Thoru, and Elizabeth Meng. Practical Guide for Clinical Neurophysiologic Testing: EEG. Available from: Wolters Kluwer, (2nd Edition). Wolters Kluwer Health, 2017. 

Greenfield, John, L. et al. Reading EEGs: A Practical Approach. Available from: Wolters Kluwer, (2nd Edition). Wolters Kluwer Health, 2020.

Theta activity is defined as a symmetrical and synchronous frequency of 4-7Hz, having a moderate amplitude of 25-50uV, with a sinusoidal morphology that is reactive to state changes. Intermittent theta mixed with alpha rhythm can be seen in a normal awake patient, especially children. 6-7Hz theta activity may be the dominant rhythm in the frontocentral regions in a young adult during the awake state that increases in the frontocentral or occipital region replacing the alpha in the context of a transition to drowsiness and is almost never abnormal. There is no definite time in brain maturation that theta activity is considered abnormal. In fact, theta is the hallmark of some normal variants.

Which normal variant is described as sinusoidal or mu-shaped theta (6 to 7 Hz) activity at the vertex region appearing in drowsiness?
Ciganek’s Theta
Correct Answer: 

Ciganek’s theta is described as having a frequency of 4-7 Hz located at the midline (vertex), seen in awake or drowsy states. This normal variant is a rhythmic, smooth, sinusoidal, arciform, spiky, or mu-like rhythm and has been described as the “midline theta rhythm” in children and adults. The original description by Ciganek found a high correlation with temporal lobe epilepsy, but later studies have found that the pattern can be seen in ¼ of the nonepileptic population.

**Fun Fact: Another type of midline theta rhythm, not at the central but at the frontal region, called the Fm theta rhythm, has been extensively investigated by Japanese researchers in relation to mental tasks, such as reading, mental calculation, etc.

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