Chapter 7

What makes EEG vary between people?

Age, level of consciousness, and brain function.

Why is EEG variability important?

Helps distinguish normal vs abnormal patterns.

What is the alpha rhythm frequency range?

8-13 Hz.

Where is alpha rhythm most prominent?

Awake, relaxed, eyes closed.

What blocks alpha rhythm?

Eye opening, attention, mental effort.

What is the average alpha frequency in adults?

~10 Hz

What alpha frequency is considered abnormal?

≤8 Hz (even in elderly).

How does alpha frequency change with age?

Increases from infancy → adolescence, then plateaus, slight decline in elderly.

What physiologic factor affects alpha frequency?

Cerebral blood flow.

What is EEG like before 3 months?

No well-defined occipital rhythm.

What rhythm appears at 1 year?

5-6 Hz theta.

When does alpha reach adult frequency (~10 Hz)?

Around 15-16 years.

Typical alpha amplitude in adults?

40-50 μV.

How does alpha amplitude differ in children?

Higher than adults.

What does very low alpha amplitude suggest?

Possible abnormality.

How does age affect amplitude?

Decreases with age.

Is alpha rhythm usually symmetric?

Mild asymmetry is common.

Which side usually has higher amplitude?

Right side.

What level of asymmetry is concerning?

>50% amplitude difference.

What is more clinically important: amplitude or frequency asymmetry?

Frequency asymmetry.

What is the typical distribution of alpha?

Posterior dominant.

Is alpha a pure sine wave?

No, shows waxing and waning.

What are “posterior slow waves of youth”?

Theta/delta waves mixed with alpha in children.

What is an alpha variant rhythm?

Alpha frequency changes (half or double).

Clinical significance of alpha variants?

None.

What is the mu rhythm frequency?

8-10 Hz.

Where is the mu rhythm located?

Central region.

What suppresses mu rhythym?

Movement (especially contralateral).

Does eye opening affect mu rhythm?

No.

Is mu rhythm symmetric?

Often asymmetric,

What is frequency range of beta activity?

14-30 Hz.

Where is beta most proiminent?

Frontal regions.

What increases beta activity?

Sedatives (benzodiazepines, barbitrates).

What does decreased beta suggest?

Cortical dysfunction.

What is breach rhythm?

Increased beta near skull defects.

What is gamma frequency range?

>30 Hz (up to ~80-100 Hz).

What functions is gamma associated with?

Cognition (attention, memory awareness).

In which conditions is gamma studied?

Schizophrenia, Alzheimer’s, and epilepsy.

What is theta frequency range?

4-8 Hz.

When is theta normal?

In small amounts, especially in younger people.

What does increased theta indicate?

Drowsiness.

Where is frontal theta commonly seen?

Young adults.

What is delta frequency range?

<4 Hz.

Is felta normal in awake adults?

No (persistent delta = abnormal).

When is delta normal?

During sleep.

What are posterior slow waves of youth?

Normal delta waves in children.

When is delta abnormal in children?

If there is high amplitude, persistent, unilateral, or not suppressed by eye opening.

What triggers lambda waves?

Eye movements with eyes open.

Where are lambda waves seen?

Occipital region.

In which population are lambda waves more common?

Children.

What happens to alpha rhythm during drowsiness?

Disappears.

What replaces alpha in drowsiness?

Theta activity.

What eye movements are seen in drowsiness?

Slow rolling movements.

What happens to muscle tone during drowsiness?

Muscle tone decreases.

What is hypnagogic hypersychrony?

Theta-delta bursts during drowsiness in children.

At what age is hypnagogic hypersychrony most common?

Around 1 year.

What are POSTS?

Positive occipital sharp transients of sleep.

When do POSTS occur?

Early sleep (Stage 1/2).

Are POSTS normal?

Yes, POSTS are normal.

What can POSTS mimic?

Epilpetiform activity.

What is the most important EEG rhythm in awake adults?

Alpha rhythm.

Most reliable abnormality indicator: amplitude or frequency asymmetry?

Frequency asymmetry.

What does slowing of alpha rhythm suggest?

Reduced cerebral blood flow or pathology.

What EEG change indicate drowsiness?

Replacement of alpha by theta.