Intro to EEG Flashcards
What do the larger spikes record in EEG represent?
Signals from muscle / eye mvmt (noise)
- measured by electrooculograms
Describe the general sense pathway from periphery to the brain
- Stimulus sensed by Nociceptor
- Nociceptor generates a signal
- signal passes through afferent nerve fiber
- synapses at dorsal horn of the spinal cord
- passes through 2nd order neuron (crosses midline at spinal cord)
- synapses in the thalamus
- passes through 3rd order neuron
- synapses in the cortex
What are the 3 measurements of the brain’s electrical activity?
- scalp –> electroencephalogram
- cortical (surface electrodes on exposed cortex) –> electrocortiocogram
- used for brain implants b/c it has the clearest and most resolute signal compared to EEG - depth (thin, needle electrodes) –> depth recording
- used to stimulate brain for invasive therapeutics
What are some general considerations when measuring the electrical activity of the brain? (2)
- complex interconnections of neuronal elements (dendrites, cell body, and axon)
- synchronization
- neurons around the same place fire together –> generate large potentials
What are some processing requirements for EEG signals? (4)
EEG: 100uV in amplitude w/ freq response of 0.5 to 80 Hz
- Work in the freq range above
- High gain to increase the small amplitude
- Large CMRR to reduce common-mode interference (common-mode voltages have serious effects in EEG signals)
- High input impedence to compensate for high source impedence (due EEG being smaller than ECG and EMG)
EEG surface electrodes are smaller than EMG’s. What is the significance of this and how do you address it?
EEG surface electrodes have higher source impedance!
- less signal is passed through the EEG electrodes
How to compensate?
- use gels to lower source impedance
- instrumentation amplifier must have higher input resistance (means that more of the signal is received by the amplifer / less signal passes the amplifier)
Compare and contrast the advantages and challenges of EEG signals
Advantages:
- mobile, inexpensive,
- safe (passive recording)
- higher temporal resolution (ms - compared to imaging techniques)
Challenges:
- low spatial resolution (compared to imaging techniques) (can’t tell where smt happens in the brain)
- interference from muscle activity in the face, eye-mvmt, neck and ears)
Compare and contrast ongoing brain activity vs evoked responses
Both are different types of data collection tests for EEG signals
Ongoing:
- used for diagnosis of epilepsy, sleep disorders, depth of anaesthesia, coma, brain death
Evoke response:
- patient performs an action and resultant EEG signals are recorded
Compare and contrast the different standardized systems for electrode positioning (2)
10 - 20 System: (adj electrodes are placed 10 - 20% of the distance from left to right or top to bottom)
- lower resolution
- faster
10 - 10 system: (adj electrodes are placed 10 - 20% of the distance from left to right or top to bottom)
- higher resolution
- slower
How to read electrode positioning charts (Letters and numbers)
Letters = brain regions:
Fp - pre-frontal
F - frontal
T - temporal
C - central
P - parietal
O - occipital
z = midline
Number = relative positions:
odd numbers = left hemisphere
even numbers = right hemisphere
small numbers = closer to midline
What are the 4 types of montages in electrode channels?
- bipolar montage
- each channel measures diff between 2 adj electrodes
- can be transverse dir or anterior to posterior dir - referential montage
- diff between 1 electrode and a refernce electrode (usually the ear or in the center) - average reference montage
- diff between 1 electrode and the avg between all other electrodes - laplacian montage
- diff between 1 electrode and the weighted avg of the surrounding electrodes
compare and contrast the different resting rhythms of the brain (4)?
- Alpha (8 - 13 Hz)
- relaxation, quiet but awake thinking
- disappears in sleep
- mostly in occipital region - Beta (14 - 30 Hz)
- alert, concentration, stress, fear and anxiety
- higher freq but lower amp than alpha
- mostly in parietal and frontal regions - Theta (4 - 7 Hz)
- REM sleep, increased memory, deep meditation, creativity, emotional stress
- mostly in parietal and temporal regions - Delta (below 3.5 hz)
- dreamless sleep, some hormone released
Compare and contrast the 3 different generalizations of epilepsy
- petit mal
a. absence - unconsciousness, twitch-like muscle contractions, blinking. (spike-and-dome signal)
b. Myoclonic - single violent muscle jerk –> can become a grand mal over time - Grand mal
- large and syncrhonous w/ alpha frequency - Psychomotor
- partial epilepsy
- consists of low freq (2 - 4 Hz) and a higher freq at (15 Hz)
How does epilepsy occur?
basal level of excitability of all or parts of the nervous system rises above a certain critical threshold
What do EEGs record?
Electrical polarity change
(aka post-synaptic dendritic currents from cortical pyramidal cells)
- caused when dendrites receive neurotransmitters from axons
What are local field potentials?
area in brain where group of nerons work together to create an amplified EEG recording
Describe the equipment used to measure EEG signals (3)
- EEG cap
- sponges (to hold saline soln)
- metal electrodes (send signals to amplifier - EEG amplifier
- Data acquisition computer (to store and analyze EEG)
What are ERPs?
Event-related potentials
- EEGs that are time-locked to a specific stimulus
(baseline = time before stimulus)
What do ERPs test for and how do they help in evaluation of those conditions?
used to test for:
- ADHD, dementia, Parkinson’s disease, multiple sclerosis, head injuries, stroke, obsessive-compulsive disorder, schizophrenia, depression
ERPs evaluate functional integrity of brain/sensory pathways
- vision, hearing, cognitive processes
- increased latency in these pathways suggests clinical abnormalities
ERPs can be used to increase objectivity in diagnosis of neurological diseases (voluntary patient response is not needed for these tests)
How do you pickout ERPs from background EEG signals
ERP has a lower amplitude (<5uV) compared to background EEG signal
Use avg techniques to minimize background EEG and artifacts
ex. adding response to N times stimulus improves SNR by factor of sqrt(N).
Describe the ERP processing steps (7)
- Cleaning / Artifact Removal
- remove artifacts (eyeball mvmt / blinks) via ref electrodes around eyes - Filtering
- ERP is low freq therefore band pass between 0.05 to 15 Hz - Epoching / Segmenting
- mark where each event occurs by extracting time windows with event codes - Baseline Correction
- correct for period that begins before event
- subtract average of baseline from each epoch - Reject extreme values
- remove epochs with too big/small or fast changing signals - Averaging trials per subject
- improve SNR
- generates an ERP that represents 1 subject - Averaging over subjects
- used to analyze large groups of subjects and understand disease / phenomena
- generates an ERP that represents a group
