EEG

Question 1

What does the EEG measure?

Answer 1

potential difference btw 2 points. It changes continuously because electric fields generated by the brain change continuously.

Question 2

How is EEG data presented?*

Answer 2

as a montage: display of data in an orderly arrangement. Shows the SPATIAL DISTRIBUTION of a changing electrical field. Odd numbers on the left, even numbers on the right.

Question 3

What generates the potentials we see in EEG?*

Answer 3

summed synaptic potentials from a large population of neurons behaving as an electrical dipole. often the cortical pyramidal cells.
Also, EPSPs and IPSPs (exitatory and inhibitory post-synaptic potentials).

Question 4

What are the groups of montages?

Answer 4

referential, where the reads are compared to a common reference, vs. bipolar, where neighboring electrodes are compared.

Question 5

What should I be aware of technincally when interpreting EEG?*

Answer 5

EEG measures very small voltages- microvoltages*. so artifacts can have a huge impact!

Question 6

What are the EEG artifacts I should consider from the environment?

Answer 6

instrumentation, electrode problems (sweat most common), electrical interference (cardiac monitors or IV pumps)

Question 7

What are the physiologic artifacts I should consider when evaluating EEG?

Answer 7

Bioelectrical: cardiac/respiratory activity
eye movements (different parts of the eye are electronegative vs positive- retina is negative, cornea is positive)
muscle movement (neuromuscular transmission and muscle contraction are EC processes)

Question 8

What physiologic factors affect the EEG?*

Answer 8

Age (newborns vs. kids. vs. teens vs. adults vs. elders)
level of arousal (wake vs. sleepy vs. sleeping)
meds (barbiturates and benzos; phenytoine, cabamazepine; lithium)
Also, there are many benign variants.

Question 9

What are some activities that may provoke EEG findings?

Answer 9

sleep, lights, hyperventilation

Question 10

What is the order of increasing frequency of the waves in eeg? what is the definition of each wave?*

Answer 10

delta: less than 4 Hz (cycles/s)
theta: 4-8
Alpha: 8-13
Beta: 13-30
DTAB: Demon Trolls Adore Brains.

Question 11

What are spikes and sharps?

Answer 11

spikes: less than 70 ms in duration -usually negative and abnormal
sharp: 70-200 ms. usually neg. sometimes normal, sometimes not.

Question 12

What is posterior dominant rhythm? What is normal? *

Answer 12

important part of the EEG. should be slower freq (alpha) and higher volatge than the anterior parts. Normal is 8.5-11.5 alpha frequency.

Question 13

What is the significance of focal slowing?*

Answer 13

focal functional abnormality

Question 14

What is the significance of generalized slowing? What else may indicate this?*

Answer 14

encephalopathy

encephalopathy may also be seen as a loss of expected organization

Question 15

What is the significance of lots of spikes and sometimes sparks?*

Answer 15

epileptic diathesis

Question 16

What is the significance of PLEDs?*

Answer 16

PLEDs= periodic lateralized eleptiform discharges. indicate destructive brain process.

Question 17

What is the significance of triphasic waves?*

Answer 17

metabolic encephalopathy; usually hepatic/renal, but may be hypoxic/ischemic encephalopathy

Question 18

For what conditions is EEG the defining test?*

Answer 18

seizures/epilepsy

state of consiousness (awake/sleep/coma/cortical death, though “brain dead” also requires death of the brain stem)