EEG Basics Flashcards
Biomarker definition and usage
Definition: Measurable indicator of biological conditions (usually presence or severity)
Usage: 1. Diagnosis; 2. Prognosis; 3. Drug development; 4. Controlling signal via BCI
Dynamic vs Quasi-static biosignal
Dynamic: modifies fast with internal or external changes (eg. Heart Rate Variability)
Quasi-static: nearly stable signals that do not change fast (eg. Body temperature)
Respiration biosignal and changes in body
Inhalation: ribs pulled up and out; diaphragm contraction; bigger lung (landing point of curve)
Exhalation: ribs in and down; diaphragm relaxation; normal-size lung (peak of curve)
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Electrooculography(EOG) biosignals
recording the movement of eye as a dipole (cornea+ positively and retina- negatively charged), both horizontally and vertically
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Electrocardiography(ECG) signal’s 3 components
- P wave: depolarization of atria
- QRS complex: depolarization of ventricles
- T wave: repolarization of ventricles
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Signal strength in Electromyography(EMG)
mainly by the amount of muscle contraction,
but these components also affect the signa:
1. electrode to muscle proximity
2. muscle to skin proximity
3. interfering tissue (e.g. fat tissue)
Ionic basis of action potential
4 Steps of action potential:
- Resting state - ~70mV membrane potential
Voltage-gated Na+ [sodium] channels closed
Voltage-gated K+ [potassium] channels closed - Depolarization phase
Graded potentials cause slight depolarization until threshold (~ -55mV) when voltage-gated Na+ channels open (voltage-gated K+ channels still closed)
Na+ rushes into the cell and membrane potential rapidly increases and peaks at about +30mV - Repolarization phase
Inactivation gate of Na+ channel “plugs” the channel, stopping K+ from entering the cell
K+ gates open allowing K+ out of the cell and membrane potential decreases - Hyperpolarization phase
Na+ channels transition from inactivated to closed
Some K+ channels are still open so the membrane potential overshoots the resting state and becomes more negative
After the original change in membrane potential» resting potential is restored
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Motor unit
the cell body and dendrites of a motor neuron, the multiple branches of its axon, and the muscle fibers that innervates it
3 levels of neuronal signal measurement
1- Single neurons (EPSP/IPSP) < by
microelectrodes inserted in neuron,
2- Neural modules (local field potentials) < by macroelectrodes in gray matter,
3- Large systemic level (EEG electrical potentials) < by scalp electrodes
Problems of signal transmission from the brain to scalp
- large portion of signals cannot pass the skull
- widely distributed topographies of cortical areas in fissures
- complex overlaps of signals because of the different angles of neural dipole arrangements (radial, tangential, oblique)
> radial neurons are the best to transmit signals
Quantitative EEG (QEEG)
A collection of quantitative methods designed to process EEG signals (spectral and wavelet analysis).
EEG vs fMRI
- EEG:
high temporal resolution => good tool to study the dynamic functions
poor spatial resolution =>poor identification of underlying neural sources - fMRI:
good spatial resolution (about 2–3 mm)
lower temporal resolution
EEG frequency bands
● Delta [0.5-4 Hz] : Sleep, dreaming
● Theta [4-8 Hz] : Drowsiness
● Alpha [8-12 Hz] : Restful, reflective
● Beta [12-36 Hz] : Active mind, busy
●Gamma [upper than 36 Hz] : Problem solving, concentration
(I also added the functions of frequencies because it was in the pictures of the slide, but they were not mentioned during the presentation)
EEG features (frequency, amplitude, phase)
- Frequency: the number of oscillations per time unit
= the number of waves you can see in 1 second - Amplitude: the strength of the pattern (microvolts)
= the height of the peaks you can see in each wave - Phase: time difference between two corresponding points on two signals represents the phase in units of time
= the temporal differences between two separate signals
Superimposed EEG signals
is when our output signal is made by 2 or more sinusoidal signals with different frequencies
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Electrode placements in EEG 1
- 10/20 system as a common arrangement for electrode placements
(the 10 & 20 in the name: referring to the 10% and 20% of the vertical/horizontal measures of the scalp that we move front-back/right-left to find the location of electrodes) - Nasion (point at the root of the nose where the frontal and two nasal bones meet)
- Inion (small protuberance on the external surface of the back of the skull near the neck)
EEG artifacts
- Internal artifacts (biological):
- Vertical eye movement (blink): in Fp1/Fp2 channels
- Lateral eye movements (eye-rolling): in F7/F8 channels
- subtle muscle activity : mostly in Frontal and Temporal
- Gross body movements (e.g. tongue or head movements)
- heart beat : in all electrodes, with its max amplitude in the left-temporal electrode and Cz-Pz
- Wet skin (e.g. sweating) - External artifacts (technical):
- Defective electrodes
- Loose electrodes
- Electromagnetic interference
- Power sources (50 Hz and 60 Hz)
Electrode placements in EEG 2
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Odd numbers (1, 3, 5) > electrodes on the left hemisphere
Even numbers (2, 4, 6) > electrodes on right hemisphere
Z (Zero) > electrodes in midline
FP > Frontal Pole
F > Frontal
C > Central
T > Temporal
P > Parietal
O > Occipital
A > Ears
Healthy sleep stages 1 : Non-REM
- N1 [Theta waves; low muscle tone; unsustained dreams; uncoupled thalamus & hippocampus from + preserved cortical interactions]
- N2 [Spindles (11-16 Hz range); K-complexes; thought-like dreams; no functional interactions btw cortical regions]
- N3[Delta waves; no cortico-cortical connections; unclear dreams]
Healthy sleep stages 2 : REM
wake-like EEG; muscle tone inhibition; saccadic eye movements (REMs); long & bizarre dreams
- Tonic-REM [Muscle atonia; high alpha & beta power; no eye movements]
- Phasic-REM [Muscle twitches; middle ear muscle activity; lower alpha & beta; eye movements]
Polysomnography
a comprehensive test used to diagnose sleep disorders
measuring (EEG, EMG, EOG, ECG, respiratory effort, oxygen saturation)
Sleep Disorders 1
Obstructive sleep apnea syndrome (OSAS)
interrupting normal breathing → interrupted sleep
Symptoms:
- Loud snoring
- Noisy breathing
- periods where breathing is interrupted
Causes :
- overweight
- male
- over 40 yrs old
Sleep Disorders 2
Narcolepsy
Chronic
Drowsiness and sudden attacks of sleep
+ can be accompanied by sudden loss of muscle tone (cataplexy)
Symptoms:
- Excessive daytime sleepiness
- Sudden loss of muscle tone
- Sleep paralysis
Causes:
- Low hypocretin levels → autoimmune reaction? genetics?
Sleep Disorders 3
Insomnia
Regular problems sleeping
Symptoms:
- Hard to go to sleep
- Waking up several times during the night
Causes include:
- Stress, anxiety, depression
- Noise
- Drugs (alcohol, caffeine, nicotine, cocaine and ecstasy)
Sleep Disorder 4
Parasomnia
Abnormal movements, behaviors, emotions, perceptions, and dreams → can occur while falling asleep, btw sleep stages, or during arousal from sleep
*NREM parasomnias:
- Sleep terrors
- Sleepwalking (somnambulism)
- Confusional arousals
- Sleep-related eating disorder
*REM parasomnias:
- Nightmare disorder
- Recurrent isolated sleep paralysis
- REM sleep behavior disorder
Causes include:
- Irregular sleep-wake schedules → jet lag, shift work
- Other sleep disorders → OSAS, narcolepsy
Sleep Hygiene
As self-treatment for Insomnia:
*Dos
- daily routine for sleep/awake
- relax 1 h before bed
- dark quite bedroom, comfortable bed
- regular exercise
*Don’ts
- no TV/phone before bed
- no smoking/drinking 6 h before bed
- no big meal before bed
- no exercise 4 h before bed
- no nap during the day
- stick to your routines!
