Lecture 2: EEG Flashcards
The cortex
- Major part of the brain
- Convolutions are the gyri and separations are the sulci.
- involved in higher brain functioning.
- divided into two hemispheres
4 different lobes
- occipital - involved in visual processing
- temporal - involved in higher meanings
- parietal - involved in spatial information processing
- frontal lobe - involved in conscious thoughts and decisions
cerebellum
- involved in the maintenance of balance and posture, coordination of voluntary movements, motor learning.
brain stem
involved in the automatic body processes
limbic system
involved in emotion, flight-or-fight
Action potentials
- Message sparks with electrical signal, this moves down the neuron – called the action potential.
- When it reaches the end of the neuron, in order to reach the other neuron, this action potential is then transformed into a chemical signal called a neurotransmitter.
- The neurotransmitter is transferred from one neuron to the next through the synapse.
- When it reaches the next neuron, a new electrical signal called the post-synaptic potential is created.
- These signals could be excitatory or inhibitory.
Pyramidal neurons
- triangular shape
- found in all the lobes
- EEG records these as they have constant shape and are perpendicular to the cortex.
EEG
Records electrical activity from pyramidal neurons on the surface.
Amplifier
Amplifier needed as signal is very weak.
Richard Caton - 1875
First recording of electrical activity in animals
- found electrical activity varies with different mental states
Adolf Beck - 1890
- found electrical activity varies with external stimuli
Hans Berger - 1924
First human EEG recording
- electrical activity varies according to functional status of brain
1936
First EEG laboratory opened
EEG pros
- Relatively cheap, compared to fMRI for example – thousands not millions.
- Portable; consists of amplifier and electrodes.
- Excellent time resolution can record every millisecond as it happens.
EEG cons
- Poor spatial resolution - Use EEG to find out when something happens in the brain, not where.
MEG pros
- Records the magnetic fields generated by neural activity
- Excellent time resolution
- Captures deeper neural activity
MEG cons
- Large, stationary, expensive
- Requires heavy maintenance, training etc.
PET pros
- Monitors metabolic activity of neurons during cognitive tasks.
- Robust towards motion artefacts.
PET cons
- Invasive – inject drug into participants.
- Poor time resolution – don’t use it to know when something happens, use it more to discover where something happens in the brain.
- Large, stationary, expensive
fMRI pros
- Measures changes in blood flow associated with changes in neural activity.
- Excellent spatial resolution.
- Not invasive – don’t have to inject anything.
- This is the best research method to find out where something happens.
fMRI cons
- Poor time resolution
- Large, stationary, expensive
oscillations
repetitive patterns of neural activity. We see these when the neurons are in synchrony.
Delta
- (1-4 Hz)
- Slow and of high amplitude.
- Known as Slow Wave Sleep (SWS): generated during meditation and deep sleep.
- Memory consolidation, healing, and regeneration are stimulated during Delta rhythm.
Theta
- (4-8 Hz)
- Generated during meditation and light sleep
- Dreaming state, beyond normal conscious awareness
Alpha
- (8-12 Hz)
- Resting state – relaxed or when we close our eyes.
- Helps mental coordination, calmness, alertness, mind/body integration, and learning
- Appears when eyes close
Beta
- (12-25 Hz)
- Normal waking state, awake and engaging in activity.
- Appears when we are alert, attentive, engaged in problem solving and decision making, focused
Gamma
- ( > 25 Hz)
- Role currently unknown
- Hypotheses:
- Expended consciousness and spiritual emergence
- Integration of various sensory impressions of an object to form a coherent form.
- By-product of other neural processes (eye-movements, micro-saccades).
What is EEG used for?
- Healthcare
- Behavioural research
- Other applications
wet electrodes
metal disks or pellets that connect with the skin via conductive gel, paste or cream, typically based on saline.
dry electrodes
easier to use, put the cap on the head, but it is much less accurate, used less in research.
number of electrodes
The choice of the number of electrodes usually depends on the purpose of the recording and, in research, on existing results and findings.
* Usually use between 32 and 128. Any more is time consuming as you have to apply the gel to each electrode individually.
Letters of electrodes
- Fp = Frontopolar region
- F = Frontal lobe
- P = Parietal lobe
- O = Occipital lobe
- T = Temporal lobe
- C = Central region
- A1 and A2 = reference electrodes
Number of electrode
- Odd number = left hemisphere
- Even number = right hemisphere.
- Z = midline region, so no number.
Why are eye electrodes needed?
To remove activity of the eyes during cleaning of the data
reference electrodes
we record the brain activity that is not associated with brain functioning, need some neutral activity.
Differential amplifier
activity from the brain Input 2: neutral activity (from reference electrodes) we subtract this activity and we get the output.
average of mastoids or earlobes - re-referencing
Take references of both mastoids or earlobes and average this. If we take activity from one side of the brain, this might affect the results – as it relates to one side of the brains activity. So, we take two references and take the average.
common average reference
don’t bother with reference electrodes, instead take all the averages of the brain and use that as the reference electrode.
electrode placement
- measure naison and inion distance, place 10+20% increments
- measure pre-auricular points, place 10+20% increments
- measure circumference, place 10%
- Join these dots and divide into 25%
Cz
- Different size of caps
- Cz is most important
- Take measure of naison and inion, and pre-auricular points
- Once found Cz, place rest of cap on
