10 EEG Basics Flashcards
Biomarker definition and application
- measurable indicator of biological conditions
- in medicine, it usually indicates presence or severity
Application - Diagnosis
- Monitoring and Prognosis (evaluate disease stage and treatment efficacy)
- biomedical research and drug development
- controlling signals to reduce symptoms via BCI learning (biofeedback and fMRI-neurofeedback)
Signal Acquisition process
- subject
- sensors
- analog processing
- analog/digital conversion
- computer
Biosignal definition and categorization
- features represented mathematically as functions of one or more independent variables carrying some information
- different origins possible (mechanic, chemical, acoustic, electric), but will be transformed into electrical signal at the end
Categorization:
- dynamic (modifies fast with internal or external changes, e.g. Heart Rate Variability) vs. quasi-static (nearly stable signals that do not change fast, e.g. Body temperature)
- permanent (e.g. EEG) vs induced (e.g. ERP) signals
Respiration biosignal and changes in body
Inhalation
- ribs pulled up and out by intercostal muscles
- diaphragm contracts and moves down
- bigger lung (landing point of curve)
Exhalation
- ribs move in and down
- diaphragm relaxes and bulges up
- lung decrease to normal size (peak of curve)
Electrooculography (EOG)
- corneal-retinal potential: eye is a dipole with cornea positively and retina negatively charged
- electrodes around eye pick up changes in potential charges according to direction of cornea
Electrocardiography (ECG)
- P-wave: depolarization of atria
- QRS complex: depolarization of ventricles (while atrial repolarization
- T-wave: repolarization of ventricles
Electromyography (EMG)
- surface vs invasive EMG
- signal strength mainly dependent on amount of muscle contraction, but other influences too (proximity of electrode to muscle, proximity of muscle to skin, interfering tissue (e.g. fat tissue))
- recording action potentials in muscle motor unit (motor unit recruitment, actioin potential recording)
Ionic basis of action potential
at rest, neurons are charged negatively (-40 to -90 mV)
- Voltage-gated Na+ [sodium] channels closed
- Voltage-gated K+ [potassium] channels closed
depolarization, e.g. via synaptic input
- voltage-gated Na+ channels open, leading to Na+-influx, that itself is depolarizing
- at threshold, process is unstoppably self-reinforcing with membrane permeability Na+»_space; K+ (towards NA+ equilibrium) and transient positivity (“overshoot”)
repolarization
- Na+-channels self-inactivate and voltage-gated K+-channels open allowing K+ out of the cell and membrane potential decreases (“undershoot”)
hyperpolarization / refractory phase
- Na+-channels transition from inactivated to closed
- some K+ channels still open so the membrane potential overshoots the resting state and becomes more negative
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 (EEG)
- Single neurons (EPSP/IPSP) by microelectrodes inserted into or near neuron
- neural modules (local field potentials) by macroelectrodes into gray matter
- large systemic level (EEG electrical potentials) by scalp electrodes
Problems of signal transmission from the brain to scalp
- Only small portion of current passes skull and returns along scalp
- dipolar activities of different brain regions appear widespread over the
scalp and generate complex overlap in EEG - ⅔ of cortex lie in fissures and lead to widely distributed topographies on the scalp (showing not radially orientation activation)
> radial neurons are the best to transmit signals
EEG, QEEG, Neurofeedback
- Electroencephalogram (EEG) is brain-related electrical potentials recorded from scalp
- Electroencephalography is set of methods of measurment and analysis of EEG
- quantitative EEG (QEEG) is collection of quantitative methods designed to process EEG signals (spectral and wavelet analysis of EEG)
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
- Gamma (> 36 Hz): Problem solving, concentration
- Beta (12-36 Hz): Active mind, busy
- Alpha (8-12 Hz): Restful, reflective
- Theta (4-8 Hz): Drowsiness
- Delta (0.5-4 Hz): Sleep, dreaming
EEG features (frequency, amplitude, phase)
- frequency: number of oscillations per time unit
- amplitude: strength of the pattern (microvolts)
- phase: time difference between two corresponding points on two signals in units of time, temporal difference between two separate signals
Electrode placements in EEG 2
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
- fragmentary and unsustained dreams
- thalamus & hippocampus uncoupled from cortex activity, while interaction between cortical areas preserved
N2
- spindles (11-16 Hz range)
- K-complexes
- thought-like dreams
- functional interactions between different cortical regions are lost
N3
- delta waves
- no cortico-cortical connections
- unclear whether dreaming occurs
