EEG Interpretation Flashcards
What is delta frequency?
3Hz or less
What is theta frequency?
4-7Hz
What is alpha frequency?
8-13Hz
What is beta frequency?
14-30Hz
What affects background frequency composition?
▪️ Age
▪️ Level of consciousness
▪️ Disease
What is the general EGG signal through childhood?
▪️ Slow frequencies
▪️ Delta-theta (increasing from birth to 3 years)
▪️ Higher voltage
How does the EEG signal change through adolescence and adulthood?
▪️ Gradual increase in frequency of posterior dominant rhythm
▪️ Becomes more organised and well-defined
▪️ Low-medium amplitude background
How does the EEG signal change through older adulthood?
▪️ Dominant alpha rhythm
▪️ Mixed in theta and beta activities
▪️ Slowing in old age
What EEG rhythm dominates eye closure?
Alpha
What happens to the EEG signal when drowsy?
▪️ Diffuse slowing and attenuation (looks more chaotic)
▪️ Delta and theta activity
What happens to the EEG signal when asleep?
▪️ Increased slowing in the background
▪️ Specific sleep phenomena indicating sleep stage
▪️ E.g. stage 3 = slow-wave sleep, delta
What are the two main types of artefacts?
▪️ Physiological (e.g., eye movement, blinking, ECG, muscle movement)
▪️ Extra physiological (e.g., faulty channel/electrode, mains interference 50Hz)
What can eye movement artefacts be useful for?
Differentiating between wakefulness and different sleep stages
(primarily frontal electrodes)
What does a 50Hz artefact indicate?
One of more electrode is poorly applied to the scalp
What might a muscle artefact indicate?
▪️ Patient is anxious/not relaxed
▪️ Chewing, tongue movement, clenching jaw
(chewing = rhythmic muscle artefact)
What are the three main activation procedures?
▪️ Hyperventilation
▪️ Photic stimulation
▪️ Sleep
(all increase likelihood of recording epileptiform activity)
What is hyperventilation and how does it affect the EEG signal?
▪️ Breathe quickly and deeply for 3 minutes
▪️ Typically causes slowing - a consequence of cerebral vasoconstriction, induced by lower CO2 levels?
What is the main EEG sign of absence seizures?
Generalised spike and wave discharges at 3Hz (3 peaks per second)
What EEG signs may be indicative of stage 2 sleep?
▪️ Brief bursts of high frequency activity - sleep spindles
▪️ Particularly in anterior channels
▪️ Absence of sinusoidal, well-defined posterior dominant rhythms
What might a rhythmic muscle artefact indicate?
Chewing
