8.11. Electroencephalogram (EEG); sleep phenomena. Learning and memory. Flashcards
I. Electroencephalogram (EEG)
1. What is EEG?
EEG is the recording of neuronal electrical activity that is produced in the cerebral cortex
I. Electroencephalogram (EEG)
2. How are electrodes placed on the skull?
- Electrodes are placed on the skull
- only the generated dipoles originating from pyramidal cells, which are perpendicular to the skull, are detected and will result in EEG waves (μV range)
I. Electroencephalogram (EEG)
3. How are temporal resolution and spatial resolution in EEG?
- Temporal resolution is very good (can detect brain activity within a millisecond timescale)
- The spatial resolution is not so good, making it harder to localize the source precisely in space
=> can increase spatial resolution by increasing the number of electrodes
I. Electroencephalogram (EEG)
4. Describe electrode placement
- 100% is measured between the naison (middle point of nasofrontal suture) and inion (occipital protuberance)
- The electrodes are placed in a way that the distance is divided in a 10% - 4x20% - 10% manner
- Can be used in the mid-sagittal and horizontal section
- 19 electrodes + reference electrodes (typically placed on ear lobes)
I. Electroencephalogram (EEG)
5A. What are the 2 types of recording in EEG?
- Bipolar recording
- Unipolar recording
I. Electroencephalogram (EEG)
5B. Describe bipolar recording
- Both the electrodes are at active site
- Difference of potential between the 2 electrodes is detected
I. Electroencephalogram (EEG)
5C. Describe unipolar recording
- One electrode is active and the other is indifferent (kept at ear lobe)
- By comparing the potential to the reference electrode, we can detect the potential at all other points
I. Electroencephalogram (EEG)
6A. What is montage?
a system in which we can detect the signals between the electrodes
I. Electroencephalogram (EEG)
6B. What are the 4 types of montage?
- Sequential monotage
- Referential montage
- Average reference montage
- Laplacian montage
I. Electroencephalogram (EEG)
6C. What is sequential montage?
difference between two adjacent electrodes
I. Electroencephalogram (EEG)
6D. What is referential montage?
potentials are compared to a reference electrode (e.g. linked
ears)
I. Electroencephalogram (EEG)
6E. What is average reference montage?
reference is the average of all signals
I. Electroencephalogram (EEG)
6F. What is Laplacian montage?
the average of the surround electrodes is subtracted
II. Basic wave types.
1. What are the 5 basic wave types
- Alpha wave
- Beta wave
- Gamma wave
- Theta wave
- Delta wave
II. Basic wave types.
2. What are the characteristics of alpha wave?
- Rhythmic, 8 – 13Hz
- Mostly on occipital lobe
- Amplitude: 20 – 200μV
- Relaxed awake rhythm with eyes closed
- Mental activityalpha waves are replaced by beta waves
- Disappears during sleep
II. Basic wave types.
3. What are the characteristics of beta wave?
- irregular, 14 – 30Hz
- Amplitude: <25μV
- Mostly on temporal and frontal lobe
- Eyes open, mental activity
- Excitement
II. Basic wave types.
4. What are the characteristics of Gamma wave?
30 – 100Hz
=> short-term memory matching
II. Basic wave types.
5. What are the characteristics of Theta wave?
- Rhythmic, 4 – 7Hz
- Drowsy, sleep
- Parietal and temporal regions in children
- Disappointment and frustration in some adults
II. Basic wave types.
6. What are the characteristics of Delta wave?
- Slow: 0,5 – 4Hz
- Often: voltages 2-4 times greater than other types of waves
- In adults: normal deep sleep rhythm
- May appear during awake state in infants
- If it appears in adults during awake state => brain tumor
III. Origin of EEG waves
1. What is the origin of EEG waves?
- Thousands/millions of cortical neurons firing in synchrony with one another
- Oscillations of EC (‘’field’’) potentials
+) Are more important for EEG signals than APs, because APs are short + fast = do not occur at the same time in different neurons -> cannot be summed (asynchronous)
+) Cellular mechanism of field potentials = alternating EPSPs and IPSPs responsible for the generation of field potentials determine the EEG waves
=> Only dipoles perpendicular to the skull are detected
III. Origin of EEG waves
2. What are the characteristics of Oscillations of EC (‘’field’’) potentials?
- Are more important for EEG signals than APs, because APs are short + fast = do not occur at the same time in different neurons
=> cannot be summed (asynchronous) - Cellular mechanism of field potentials = alternating EPSPs and IPSPs responsible for the generation of field potentials
=> determine the EEG waves
IV. Mechanism of generation of field potentials
1. Describe the mechanism of generation of field potentials
- An ascending excitatory axon will form a synapse with the dendrite of a pyramidal neuron
- Glutamate is released and AMPA-R in the dendrite will open, as a result there will be an influx of positive charges (Na+-influx)
-> local depol. of the dendrite
-> positive charges will move from EC space to the dendrites
-> EC space becomes negative (current sink) - There will be a current within the cytoplasm toward the cell body
-> cell body will become little bit depolarized
-> outward K+-current
-> the EC space around the cell body will become positive and negative inside the soma (current source)
IV. Mechanism of generation of field potentials
2. What are the characteristics of Positive EEG wave?
- Apical IPSP
- Perisomatic EPSP (near soma)
IV. Mechanism of generation of field potentials
3. What are the characteristics of Negative EEG wave?
- Apical EPSP
- Perisomatic IPSP
=> The cellular mechanism cannot be unequivocally determined from the polarity of the EEG wave
IV. Mechanism of generation of field potentials
4A. Only synchronized PSPs induce detectable EEG waves
-> T/F?
True
IV. Mechanism of generation of field potentials
4B. Only synchronized PSPs induce detectable EEG waves
-> Explain
- Individual neurons produce characteristic EPSPs and IPSPs in a synchronized manner
- Under these conditions, the electrical activity form these neurons is summed -> signal strong enough to be detected on the surface
- Thalamus is a very important factor in this synchronization process
V. Describe Mechanisms of synchronizations
- Different neural circuit can oscillate in the same frequency range -> when we detect an EEG wave, we cannot be entirely sure which system caused it
- Example:
+ Thalamic delta rhythm: in deep sleep
+ Cortical delta: surgical removal of the thalamus -> enhancement of neocortical delta
activity
=> Thalamocortical oscillations are important in alpha rhythm
VI. Thalamocortical synchronization
1. Describe Thalamocortical synchronization
- Relay nuclei and the nucleus reticularis thalami are interconnected in the thalamus
- These interconnections may be responsible for the oscillations, which are transmitted to the cortex
- There may also be oscillations between the cortex and relay nuclei, because the cortex will send many fibers back to the thalamus
VI. Thalamocortical synchronization
2. What is network oscillation?
one set of neurons interact with another set of neurons, and the
activity oscillates in these 2 populations
VI. Thalamocortical synchronization
3 What is Recurrent collateral inhibition?
if one neuron population is activated, this activity
(after a delay), will inhibit the same neuron population – inhibitory interneurons are
involved
=> there is an activity followed by an inhibition
VI. Thalamocortical synchronization
4. What is Post-inhibitory rebound?
if the neurons are inhibited for a time period, they will become spontaneously activated after the inhibition disappears
VII. Evoked potentials
1. Describe evoked potentials
- Normal EEG recording => spontaneous potentials
- Evoked potentials => following presentation of a stimulus
- ERP: event-related potentials = time-locked to some ‘’event’’
+ auditory evoked potentials (AEPs): e.g. clicking sound
+ visual evoked potentials (VEPs): e.g. pattern-reversal checkerboard
+ somatosensory evoked potential (SSEPs): e.g. peripheral nerve stimulation