Neurology Flashcards
What is EEG?
electrical activity of the brain measured on the scalp surface
Pyramidal neuron
Span entire cortex
Radial
Lined up in same direction - vertically oriented
Create circuit in layer around cell as different parts of the cells have different electric potentials
EPSP
Excitatory postsynaptic potential
movement of ions, positive change, more electrically excitable
big enough change generates an AP
generated at same time
IPSP
Inhibitory postsynaptic potential
movement of ions, negative change, less electrically excitable
big enough change generates an AP
generated at same time
Current source
Current (positive ions) flows out of cells
Current sink
Current (positive ions) flows into cells
Co-ordinated EPSP generates sink
Dipole
- One surface negative
- Corresponding area of surface positive
- Depends on orientation of the EEG source
Name the 4 lobes of the brain and their function
Frontal: higher executive function, decision making
Parietal: processing sensory info
Temporal: speech, language, learning, memory
Occipital: processing visual info
Cerebral cortex
Most EEG gerentating regions at surface (scalp EEG)
Grey matter at top
Large surface area: many bulges (gyri) and deep furrows (sulci) - allows for more neurons
Sulci & gyri
sulci = deep groove
gyri = bumps and ridges in cerebral cortex
How many layers does the cerebral cortex have?
6
What type of neurons generate EEG?
Pyramidal neurons
What is the primary cause of epileptiform spikes?
paraoxysmal depolarising shifts
Paraoxysmal depolarising shifts
Sustained period of neuronal depolarisation
What type of cells and in what region of the brain generate EEG rhythms?
Pacemaker cells in thalmus
(pacemaker cells drive the reactions
Why is it that EPSPs/IPSPs can be measured in EEG but APs can’t?
EPSPs/IPSPs: last 5-20ms
APs: last 1ms
How do Pyramidal Neurons and EPSPs relate to EEG generation?
inside of cell more positive,
outside more negative,
loop of current flowing,
surface negative potential can be measured,
flow of EPSPs all together create a large enough current to be measured on the scalp
Cl- & K+ are EPSPs or IPSPs?
IPSPs
Ca2+ & Na2+ are EPSPs or IPSPs?
EPSPs
Name the 6 layers of cerebral cortex
Layer I: Molecular layer
Layer II: External granular layer
Layer III: Extrenal pyramidal layer
Layer IV: Internal granular layer
Layer V: Ganglionic layer
Layer VI: Multiform cell layer
(surface in)
Depolarisation induced by neurotransmitter - EPSP or IPSP?
EPSP
Hyperpolarisation - EPSP or IPSP?
IPSP
Electrode types for EEG (3) + examples of each
EEG Surface Electrodes: Ag/AgCl, Au, Pt
Supplementary electrodes: ECG, EOG, EMG (deltoid)
Special EEG Electrodes: subdermal needle, nasopharyngeal
Most common EEG electrode
Ag/AgCl surface electrode
Types of EEG surface electrodes (3)
Disposable
Reusable
Caps
Electrode application for EEG
Adhesives: - conductive paste for routine EEG
- Collodion longterm EEG studies
Skin Prep (NuPrep): lower electrode impedance
Electrode placement for EEG (4)
10-20 system (10%/20% of total size of head)
-measurement: use china marker & disposable tape
-anatomical landmarks: nasion/inion &preauricular points
-electrode nomenclature: letter & number
Anatomical landmarks for 10-20 system (2)
nasion/inion (anterior - posterior)
preauricular points (transverse)
Electrode nomenclature: letter system (5)
F = frontal
C = centre
P = parietal
O = occipital
T = temporal
Electrode nomenclature: number system (3)
Right side: even number
Left side: odd number
Centre: z
10-20 system: views (3)
Saggital plane (side view)
Horizontal plane (top view)
Coronal plane (front view)
Ideal electrode impedance on EEG
<5kohm
Min electrode impedance on EEG
<10kohm
What does a higher amplitude of electrical impedance indicate?
More artefact
What is the purpose of electrical impedance?
Measure integrity of each electrode
Amplifier (EEG)
capture signal, amplify, and convert to digital for computer processing purposes
Display (EEG) (2)
Amplitude (vertical scale) - sensitivity control, commonly set at 7-10microV, high amplitude activity = decreased sensitivity
Time (horizontal scale) - sweep speed (30mm/s), 15s/page of EEG
Filters (EEG) (4)
Purpose: attenuate frequency, enhance region of interest
Types:
Low Pass Filter (0.5Hz)
High Pass Filter (70Hz)
Notch Filter (50Hz)
What type of high frequency signal would be filtered out in a low pass filter?
Sweat, respiration
What type of low frequency signal would be filtered out in a high pass filter?
Muscle movement, electrical noise
What type of signal would be filtered out in a notch filter?
AC Mains Supply
Time constant (EEG)
time (s) it takes for a signal to decay to 37% of it’s initial amplitude when a square wave is applied to the input terminals
Aliasing (2)
Occurs when system measured at inefficient sampling rate
Creates frequency misinterpretation of recorded signal
Montage
Arrangement of electrodes used in recording
Location of maximal potential / region of interest found most easily on EEG by…
phase reversal
Bipolar montage
Serial pairs of electrodes compared with each other to record difference between each pair
Bipolar montage: Bipolar longitudinal
aka Double Banana
useful to view symmetry between left and right hemispheres
can determine potential gradient in anterior-posterior direction
Bipolar montage: Transverse
side by side
useful to determine if activity has temporal / parasagittal dominance
What type of montage is useful in sleep studies & why?
Transverse
Centre line active in sleep
Vertex waves seen
Referential montage
multiple scalp electrodes (input 1)
connected to common reference (input 2)
Common referential montages
To Mastoid (A1/A2)
To Vertex (Cz)
External point (neck to cervical)
Avg reference
Assumption of referential montage
Reference electrode assumed electrically inactive
Activations in EEG (3)
Hyperventilation
Photicstimulation
Sleep/sleep deprivation
Hyperventilation EEG Activation
Rate of 3-4 breaths / 10s
3 mins
Children use a pinwheel
Expected EEG for Hyperventilation EEG Activation (2)
Bilaterally diffuse synchronous slow wave bursts
Theta > Delta “HV buildup”
Contraindications for Hyperventilation EEG Activation
Recent stroke, TIA, pregnant, >65y/o, recent cardiac/resp issues
Photicstimulation EEG Activation
Performed to elicit a photoparoxysmal response (PPR) for diagnosis of photosensitive epilepsy
- Strobe Light
- Distance 30cm from patient
- Repetitive flashing light – 10 seconds on/off
- Frequency 2Hz-20Hz, 50Hz, 30Hz, 25Hz
- Eye opening and eye closure for each flash frequency
Sleep/sleep deprivation EEG Activation
Increases the diagnostic yield of EEG
Enhances generalised discharges > focal discharges
Unclear if sleep deprivation or sleep itself is the true activator
EEG artefact
Anything recorded no cerebral in origin
EEG artefact examples (2)
Physiological/Biological origins
Nonphysiological (electrical) origin
EEG Waveform (4)
Frequency & Amplitude
Location: which region of the brain is affected? Occipital? Posterior vs Anterior?
Symmetry
Responsiveness: change with a given action? e.g. eye opening
EEG Frequency (4)
Alpha 8-13Hz eyes closed, awake
Beta >13Hz awake
Theta 4-8Hz
Delta 0.5-1Hz
EEG Amplitude
Find which channel amplitude is highest in - referential montage
EEG Location
Phase reversal & max amplitude
What electrode is this happening in?(find common)
Phase reversal
Find pair of electrodes (2 channels) where EEG signal changes direction Phase reversal in a bipolar chain
OR
Find which channels amplitude is highest in
Phase reversal at B
Posterior lead: posterior dominant
Symmetry in EEG (2)
Synchronous & Symmetrical (same in both hemispheres)
Normal adult EEG (5)
Alpha Rhythm
Posterior dominant
Blocked eye opening
Mu Rhythm
Lambda waves
Lamda Waves
awake state (seen on eye opening)
small triangular ‘sail-like’ shapes
small ‘evoked potentials’
Mu Rhythm
common in children and YAs
f ~9Hz
central regions - unilateral
blocked by movement of contralateral limb
Sleep EEG - stages (5)
Drowsiness
N1
N2
N3
REM
Sleep EEG - characteristics (6)
Drowsiness
N1/stage 1: alpha loss, vertex sharp waves (CZ)
N2/stage 2: vertex sharp waves, K spindles
N3: spindles & delta
Stage 4: deltas
REM: alpha, visible eye movements
Delta wave progression through sleep stages
Increases as sleep stages increase
What sleep stage is not reached in EEG lab?
REM
Vertex sharp waves
Located to vertex
Cz-High amplitude
Broad-V-shaped
Striking features of light sleep
K complexes
Sharp wave+Slow wave+ spindle
Stage 2/N2 sleep
Maximal in vertex/mid-line
Coma
Increased theta activity
Increased delta activity
Supression burst
Isoelectric
Abnormal theta, delta, discontinuity
Pathological features in coma (5)
- Periodic lateralized epileptiform discharges (PLEDS)
- Triphasic complexes
- Asymmetry
- Dysynchrony
- Extreme delta brush
PLEDs (4)
Periodic lateralized epileptiform discharges
- Represent acute focal neurological disturbance
- Stroke
- Focal Infection-Herpes Simplex
- Focal inflammation-Auto-immune encephalitis
Triphasic Complexes (4)
- Characteristic of a wide range of encephalopathy
- Hypoxia
- NH3 (Liver)
- Uraemia (Kidney)
Extreme Delta Brush
Delta
Super-imposed higher frequency activity
Associated with anti-NMDA encephalitis
EEG in children (4)
EEG changes as children get older (up to 20 y/o)
Decreasing EEG activity as age increases
Delta initially decreases in first 3 yrs
Some theta
Dominant rhythm increases as age increases
EEG in children - specific to children (2)
Alpha sub-harmonic
Posterior slow waves of youth
