Fisch EEG Primer Chapter 11 Flashcards
The normal EEG of wakeful resting adults of 20-60 years of age
This type of rythym consists of sinusoidal waveforms >8H and <13Hz maximal over the posterior head region and is typically blocked by eye opening and disappears during drowsiness and sleep
The alpha rythym
This rythym consists of waves >13Hz in either a wide distribution or limited to frontal or posterior head regions; should disappear during later stages of sleep; typically of lower amplitude than alpha
The beta rythym which is almost always a GOOD prognistic sign (requires normal cortical function) - can be caused by benzos/barbs
Mu rythym (can be precipitated by scanning visual images) consists of…
seen in less than 5% of EEGs, arch-shaped 7-11 Hz of trains over central to central parietal regions typically in younger adults.; best seen on bipolar montage when alpha is blocked by eye opening
NOTE:previously known at ‘wicket’, ‘comb’, or ‘arceau’ rythym
Lambda waves (can be precipitated by looking at images containing a lot of detail) consist of…(morphology, duration, phase, amplitude
- sawtooth shaped and positive polarity occurring primarily in occipital regions - look like POSTs
- 100-250 ms
- typically diphasic
- 50microV
- marked asymmetry is abnormal to lower amplitude side
- may be a physiologic VEP since waveform, delay, etc. same pattern
Vertex sharp transients (V waves) consist of…
sharp transients of negative polarity at the vertex -commonly seen in sleep
NOTE: may be seen in awake adults/children after startle response
Kappa rythym consists of…
bursts of very low amplitude waves of alpha or theta frequency seen in temporal region that are seen in subjects engaged in mental activity
Intermittent posterior theta rythyms…
are more rare than alpha or beta rythyms;
low voltage activity can sometimes be modified through the following activating procedures
hyperventilation, photic stimulation and sleep - low voltage EEG is considered abnormal if altered from baseline
Alpha rythym that never exceeds 8 Hz is…
always abnormal
Alpha rythym may decrease by approximately 1 Hz during…
drowsiness
NOTE: alpha rythym should be a constant value throghout life (same on serial recordings), decreases of 1Hz or more during adult life if abnormal even if the absolute value is still within the normal range.
What is the phenomena of alpha rythym temporarily increasing by 1 Hz during eye closure and then rapidly returing to baseline
squeak phenomena
What is the accepted range of frequency difference between the hemispheres
SHOULD BE THE SAME FREQUENCY, even slight difference if difference is persistent considered definitely abnormal (lower frequency hemisphere is abnormal)
NOTE: alpha frequencies do not need to be in phase
Alpha frequency activity in the Fp1 and Fp2 regions..
is artifact until proven otherwise
Asymmetric alpha amplitude typically follows this pattern…
right alpha rythym is typically of higher amplitude, left alpha rythym should be at least 50% of that on right. - may be caused by different thickness of occipital bones
NOTE: occasoinally higher amplitude is seen on the left
What is Bancaud’s phenomena?
Unilateral blocking of the alpha rythym