EEG: principles; ERPs & time-domain Flashcards
Pioneer of EEG
Hans Berger
Neural basis of EEG (2)
- Post-synaptic potentials (PSPs) in apical dendrites create a dipole towards the soma of the cell
- Modulations in extracellular currents due to PSPs are captured by EEG from the scalp
Which EEG rhythms are visible with the naked eye?
Alpha and Beta
What does EEG signal depend on?
- Orientation of dipole
–> EEG is especially sensitive to perpendicularly oriented dipoles generated in pyramidal neurons in the gyri
2. Location of synaptic activity
–> Excitatory input near the soma creates positive EEG deflections
–> Excitatory input at apical dendrites creates negative EEG deflections
3. Neural synchrony
–> Amplitude of the EEG is modulated by the amount of synchrony in a local population of neurons
What does the EEG signal amplitude depend on?
Amplitude is modulated by the amount of synchrony in a local population of neurons
Advantages of EEG
○ High temporal resolution (ms range)
○ Good for studying dynamic processes
○ Non-invasive
○ Relatively cheap (compared to MRI)
○ Light-weight, can even be portable
Disadvantages of EEG
○ Poor spatial resolution
○ Limited depth sensitivity (only outer layers of brain measures)
○ Susceptibility to artifacts
○ Difficulty in measuring activity from small populations of neurons
○ Long set-up time
General EEG working principle:
EEG measures the summed up activity of thousands of parallel-oriented, neighbouring and synchronously active pyramidal neurons (cortex layer 5 and 6)
EEG artifacts:
- Eye movement artifacts, e.g., saccades, blinks
- Muscle artifacts, e.g., clenching of jaw
- Heartbeat
- Slow drift, caused by e.g., sweating
Pre-processing filters:
- High-pass filter (0.01 Hz) - removes low frequencies, like slow drifts, breathing
- Low-pass filter (e.g., 40 Hz), removes muscle (EMG) artefact, or electrical interference from nearby electronic devices.
What do F, P, T, O, Z and C mark in EEG electrode placement?
■ F - frontal lobe
■ T - temporal lobe
■ Z - midline
■ P - parietal lobe
■ O - occipital lobe
■ C - Central sulcus
Types of ERP components?
- Early components (‘exogenous’)
- Later components (‘endogenous’)
What are early EEG components?
- Automatic sensory responses of the brain, usually in first few ms after event/stimulus
- Key: Short duration, high amplitude, and specific topographical distribution over the scalp
- Highly influenced by physical stimulus properties
- Clinical use (e.g., test integrity of sensory pathway)
- Can also be modulated by emotion, mood, attention, reward etc.
- e.g., P1, P2, N1
What are later EEG components?
- Reflect internal, high-order processing, such as attention, memory, and decision-making
- Occur after the early components have peaked
- More distributed and diffuse scalp distribution
- e.g., P3 (or P300), which is often observed in response to an infrequent or unexpected stimulus
Explain the power spectrum of EEG
It follows the 1/f Law, meaning that the power of the EEG signal is relatively high at low frequencies (e.g., delta and theta bands) and gradually decreases as frequency increases (e.g., alpha, beta, and gamma bands).
