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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