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
Superimposed EEG signals
- output signal is made out of 2 or more sinusoidal signals with different frequencies
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
any component of EEG signal not directly produced by brain activity
Internal artifacts (biological):
- vertical eye movement (blink): in FP1/FP2 channels
- Lateral eye movements (eye-rolling): in F7/F8 channels
- subtle muscle activity (EMG): 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
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
Healthy sleep stages 2 : REM
- wake-like EEG, hippocampal theta rythm accompanied by cortical activation with fast gamma waves (>= 35HZ)
- inhibition of muscle tone
- saccadic eye movements (REMs)
- long, bizarre, hallucinatory dreams
- Tonic REM: muscle atonia, increase in alpha & beta oscillations, no eye movements
- Phasic REM: muscle twitches, middle ear muscle activity, decreased alpha & beta osciallations, 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)
- walls of throat relax and narrow during sleep, interrupting normal breathing -> interrupted sleep
Symptoms:
- Loud snoring
- Noisy breathing
- repeated short periods where breathing is interrupted
Causes :
- overweight
- male
- over 40 years old
treatment:
- lifestyle changes
- continuous positive airway pressure (CPAP) device
- mandibular advancement device (MAD)
Sleep Disorders 2
Narcolepsy-cataplexy syndrome
- Chronic -> overwhelming 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?
treatment:
- stimulants
- antidepressants
- sodium oxybate
Sleep Disorders 3
Insomnia
- Regular problems sleeping
Symptoms:
- finding it hard to go to sleep
- Waking up several times during the night
- lying awake at night
Causes:
- Stress, anxiety, depression
- Noise
- Drugs (alcohol, caffeine, nicotine, cocaine and ecstasy)
treatment:
- changes in sleeping habits
Sleep Disorder 4
Parasomina
- abnormal movements, behaviors, emotions, perceptions, and dreams → can occur while falling asleep, between 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
treatment:
- good sleep hygiene habits
- hypnosis, relaxation therapy, cognitive behavioral therapy (specific to NREM parasomnias
- clonazepam and melatonin (specific to REM parasomnias)
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!
