EEG - Electroencephalography Normal EEG Waveforms Questions and Answers 1 — Questions and Answers
Question 1: An EEG recording of a relaxed, awake adult with eyes closed shows a prominent 8-13 Hz rhythm in the occipital regions. This rhythm attenuates with eye opening. Which of the following best identifies this waveform?
- Mu rhythm
- Beta rhythm
- Alpha rhythm (Correct answer)
- Theta rhythm
Correct answer: Alpha rhythm
The posterior dominant alpha rhythm is the hallmark of a normal, relaxed, awake adult EEG with eyes closed. It is characterized by its frequency of 8-13 Hz, posterior location (maximal in the occipital regions), and its attenuation or blocking with eye opening or mental effort.
Question 2: During a routine EEG on a 25-year-old patient, the technologist observes intermittent bursts of 7-11 Hz, arch-shaped waves over the central head regions (C3, C4, Cz). This activity disappears when the patient is asked to make a fist. What normal EEG variant is being described?
- Lambda waves
- Mu rhythm (Correct answer)
- Sleep spindles
- Posterior slow waves of youth
Correct answer: Mu rhythm
The Mu rhythm is a normal variant found in the alpha frequency range (typically 7-11 Hz) with a characteristic arch-like or comb shape. It is located over the central regions (sensorimotor cortex) and is uniquely blocked or attenuated by contralateral motor activity, the thought of movement, or tactile stimulation, but not by eye opening.
Question 3: A technologist is reviewing an EEG from an awake patient who was asked to scan a complex image. The recording shows bilateral, positive, sharply contoured waves in the occipital channels that occur only during the visual scanning task. These waveforms are most likely:
- Positive Occipital Sharp Transients of Sleep (POSTS)
- Epileptiform discharges
- Vertex waves
- Lambda waves (Correct answer)
Correct answer: Lambda waves
Lambda waves are normal, waking phenomena that are time-locked to saccadic eye movements, such as those that occur during visual scanning or reading. They are characteristically positive in polarity, have a sharp or triangular shape, and are located in the occipital regions.
Question 4: Which of the following statements is true regarding beta activity in a normal adult EEG?
- It is typically highest in amplitude in the occipital regions.
- It is defined as activity in the 4-7 Hz frequency range.
- It is often enhanced fronto-centrally by drowsiness or certain medications like benzodiazepines. (Correct answer)
- It is always considered an abnormal finding in an awake adult.
Correct answer: It is often enhanced fronto-centrally by drowsiness or certain medications like benzodiazepines.
Beta activity (>13 Hz) is a normal rhythm, typically low in amplitude and most evident in the frontal and central regions. Its amplitude can be enhanced by a state of drowsiness or by the use of sedative-hypnotic drugs, such as benzodiazepines and barbiturates.
Question 5: In a healthy, awake adult, the presence of excessive, generalized, and persistent theta activity (4-7 Hz) would most likely be interpreted as:
- A normal variant during hyperventilation.
- An indicator of deep relaxation.
- A normal posterior dominant rhythm.
- Evidence of cerebral dysfunction. (Correct answer)
Correct answer: Evidence of cerebral dysfunction.
While small amounts of theta activity can be normal, especially during drowsiness, excessive and persistent generalized theta activity in an awake adult is considered abnormal. It is a nonspecific indicator of generalized cerebral dysfunction or encephalopathy.
Question 6: The posterior dominant rhythm (PDR) in a healthy 8-year-old child is expected to have a frequency of approximately:
- 4-5 Hz
- 6-7 Hz
- 9 Hz (Correct answer)
- 11-12 Hz
Correct answer: 9 Hz
The frequency of the posterior dominant rhythm matures with age. It starts around 3-4 Hz in infants, reaches 8 Hz by about age 3, and typically achieves a frequency of 9 Hz by age 8. It stabilizes in the adult alpha range of 8-13 Hz in the early teen years.
EEG - Electroencephalography Normal EEG Waveforms Questions and Answers 1
An EEG recording of a relaxed, awake adult with eyes closed shows a prominent 8-13 Hz rhythm in the occipital regions.
This rhythm attenuates with eye opening.
Which of the following best identifies this waveform?