Normal EEG Activity-Part 1
NDT 101 Lecture Notes Fundamentals of EEG Technology, Volume 1 Chapter 14
Terms in this set (96)
How do you learn what is "abnormal" in an EEG?
first learn what is "normal" and become an expert in "normal"
Many normal features in an EEG can be mistaken for what?
What do misinterpretations of an EEG lead to?
Is "normal" the same for all patients?
Essential characteristics of an EEG
-frequency or duration
-regulation of frequency and voltage
-manner of occurrence
What is meant by "manner of occurrence"?
What does inter hemispheric coherence involve?
Why is the age of a patient important in regards to an EEG?
-EEG patterns vary considerably with age
-breakdown to weeks of CA (1-3 months)
-months of age (4-36 months)
-years of age (3 years and up)
Why is the "state" of a patient important?
-important for interpretation
-what's normal for one state of consciousness can be abnormal for another
What are the various "states" of a patient?
how the EEG patterns react to stimuli
Stimuli used to test "reactivity"
-eyes open/eyes closed
-repetitive movements of the extremities
-hypocapnia during HV
CO2 levels decrease because it's removed faster than it's produced because of hyperventilation
REACTIVITY: Eye opening is the primary cause of...
REACTIVITY: What is blocked during concentrated mental effort?
REACTIVITY: What percentage of young adults don't block?
REACTIVITY: What are causes for failure to block on one side?
-cerebral dysfunction or lesion
-non-reactive side suspected pathology
Testing reactivity will...
-determine if EEG is abnormally slow or if patient is drowsy
-determine if high-volatage waves seen in children are normal arousal activity or abnormal
-determine if both hemispheres show lambda
What region shows maximal alpha rhythm and in what percentage of adults and children?
What is the exception to "distribution"?
32% adults have other alpha distributions than in the occipital regions
-both central and temporal
What is the starting point for visual analysis?
What is alpha rhythm also known as?
normal background pattern
What is the frequency of alpha waves?
What age do alpha patterns begin at?
3 years old
What is the frequency for alpha with most people?
What is the dominant region we see alpha waves in?
What can alter the speed of alpha waves?
What age does alpha waves usually slow down in?
"late in life"
When does alpha reach maximum frequency?
What "flow" is alpha related to?
Good cerebral blood flow equals...
good alpha waves
What group has really good frequency regulation?
In young people, what does the mean frequency vary in regards to alpha regulation?
-not more than 5 Hz
-voltage regulation does not apply
Same subject alpha variations
-time of day
ALPHA REGULATION: increase age equals...
less well regulated
ALPHA VOLTAGE: Scalp recordings
-voltage is variable
-6-7% normal humans have less than 15 uV alpha
-voltage is exponentially increased with increased inter-electrode distance
Alpha voltage in children
-usually high voltage alpha
-low voltage, <30uV, in only 1.3% of sampled population
-high voltage, 100uV, alpha not considered abnormal
ALPHA VOLTAGE: Why does voltage decrease with age?
-density of bone
-increased tissue impedance
Intracranial recording show what kind of voltage?
high voltage alpha
When does "alpha" background reactivity begin?
What does "alpha" background reactivity read at 5 months old?
What does "alpha" background reactivity read at 12 months old?
What does "alpha" background reactivity read at 36 months old?
8 Hz in 82% of normal children
What is the reading for mean alpha at 9 years of age?
9 Hz in 65% of children
What do you do to see alpha during wakefulness in small children?
force eyes closed
What are the changes in alpha in the elderly?
-slows gradually after age 58
-increased diffuse slow
-develop focal dysrhythmias
Different studies not all patient specific, in the elderly, who has well preserved alpha?
-seniors with active lives and active minds
-retired librarians and teachers
-slowest activity, 0-3 Hz
-normal in sleep for children & adults
-focal is abnormal
-bilateral is abnormal
-bilateral is abnormal in awake adults
Normal theta activity in young adults
-6-7 Hz random activity (less than 25 uV)
-slower than 6 Hz is abnormal
-frontal or frontocentral regions
-with eyes closed
-in the presence of alpha
-drowsiness accentuates this in occipital region
High voltage theta (>100uV) is considered abnormal if
-found in adults
-found in children not HVing
-found in children if awake and clearly not drowsy
High voltage theta (>100uV) is considered normal if
-children are drowsy
-in HVing children or adolescents
In young adults and children, what enhances frontal rhythmic theta to 6-7 Hz?
heightened emotional states
In young adults and children, when is marked frontal rhythmic theta activity seen?
with eyes open and while performing tasks
In young adults and children, according to Ebersole & Pedley 2003,
there is no clear cut end point at which formal theta activity can be specified as abnormal
When are children prone to increased theta activity?
during highly emotional states (not considered pathological)
BILATERAL SYMMETRY: Is asymmetry of alpha, common or uncommon?
BILATERAL SYMMETRY: What percentage of adults have asymmetry?
BILATERAL SYMMETRY: What percentage of adults with asymmetry have right handed dominance?
BILATERAL SYMMETRY: Asymmetry is about what percentage voltage difference?
BILATERAL SYMMETRY: Is greater than 20% voltage asymmetry rare or common?
BILATERAL SYMMETRY: Voltage asymmetry of >50% is considered
BILATERAL SYMMETRY: What percentage of children have asymmetry of 20%?
BILATERAL SYMMETRY: In children, which hemisphere is lower voltage in 98% of the 95% of children that have asymmetry of 20%?
BILATERAL SYMMETRY: Which side of the skull is thicker?
BILATERAL SYMMETRY: Skull thickness is thought to account for what percentage of voltage asymmetries?
BILATERAL SYMMETRY: Abnormalities relating to asymmetry
->50% asymmetry is significant/abnormal
-rule out inter electrode distance errors first
-leakage during infusion to scalp vein
ALPHA VARIANTS: Abrupt alpha phase reversal
-resultant waves appear half frequency
-may appear unusual or abnormal
-it is normal
ALPHA VARIANTS: Harmonics
-physiological variation of the basic cortical rhythm
-sub-harmonic = slow alpha variant
-harmonic = fast alpha variant
-random sporadic or predominant
-no correlation with clinical entity
As a tech your job is to obtain the best
Parameters for optimal recording conditions
-quiet recording environment
-non-stressful recording environment
-patient at rest but awake
-patient stop talking
-fast low voltage of 13 Hz and higher
-14-16 Hz band
-18-25 Hz band
-35-40 Hz band
Beta is commonly present in what population?
normal adults and children
What region is beta found?
pre-rolandic (frontal), post-rolandic (posterior) most common or generalized
Beta's amplitude is normally low, reading at
What is beta high amplitude considered?
25uV and greater
Beta that is higher than 25uV is considered
abnormal but of no diagnostic utility
What band of beta is primarily effected by drugs?
18-25 Hz band
What drugs commonly effect beta activity?
What response does beta have to the drugs that effect it?
increase in amplitude and the amount of beta
What enhances beta activity?
Drowsiness and sleep beta changes in the 18-25 Hz band
-increases in light sleep
-increases in REM sleep
-decreases in deep sleep
What activity shows the same frequency in both hemispheres?
In beta, asymmetry as high as 35% is considered to be
In beta, >35% asymmetry indicates
-subdural or epidural fluid collection
Beta activity in the 14-16 Hz band
-primarily seen frontal and centrally
-usually enhanced by HV
Beta activity in the 35-40 Hz band
-rarely seen in scalp recordings
-depth recordings show beta up to 50 Hz
-enhanced during stages 1 and 2 of sleep
-decreases in deeper sleep
Increased beta in children during sleep
-rule out drug effect
-mixture of 18-25 Hz band & 14-16 Hz band
-"sigma" activity in the 10-14 Hz band
"Sigma" activity in the 14-16 Hz band
-abnormal finding (cerebral palsy, mental retardation, "extreme spindles")
What activates the beta pattern?
-enhanced with drowsiness
-enhanced with medication or drug use
What is the beta frequency on the scalp?
What's the duration of beta?
reciprocal of the frequency
What is considered normal typical voltage for beta?
less than 25 uV to be normal
What is the morphology of beta (wave shape)?
small fast sinusoidal
Does beta occur in bursts, trains, sporadically or continuously?
What other patient condition relate to the beta pattern?
medications or drug use (barbiturates) enhance it