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Principles of CN Proper > Lecture 3: EEG > Flashcards

Lecture 3: EEG Flashcards

1
Q

Diagram of measurement and manipulation techniques in CN

A
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2
Q

Neuroscientists are interested in the relationship between

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brain and behaviour

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3
Q

EEG and MEG are electrophysical measurements which means measurement…. looks at (2)

A

the measurement of the electrical activity, or “excitability”, of biological cells

Look at electrical and magnetic fields in the brain

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4
Q

Neurons produce electrical charges in brain such as - (2)

A
  • Producing AP
  • Electrical current flows down neurons (dendrites) - post-synaptic potentials
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5
Q

What does this diagram show?

A

Pyramidial cell , type of neuron in brain, with information (i.e., current due to the way it pulls ions in/out of cell) it pulls flowing down it

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6
Q

What is the effect of electrical current flowing down the dendrite?

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The tissue near the dendrites becomes negatively charged and the tissue around the cell body positively charged

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7
Q

We can measure neuron’s electrical charges in brain it produce via

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intracranial recordings

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8
Q

2 ways of doing intracranial recordings - (2)

A
  • Single unit recordings (/depth electrodes/stereo EEG)
  • Electrocorticography (ECoG) = grids of electrodes
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9
Q

Single-unit recordings can also be called.. (2)

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depth electrodes
stereo EEG

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10
Q

Stero in Stero EEG means

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surgically implanted electrodes

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11
Q

Diagram of depth electrodes in brain

A

3 separate Electrodes are deep into the brain (specifically temporal lobe)

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12
Q

Situations where you can do intracranial recordings - (2)

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  • Animals where they removed top of head and electrodes surgically implanted and rewarded when completed visual task (what activity of neurons happens when complete task)
  • Epileptic patients before suregrey to find where in the brain its causing the seizure to remove it surgically and where in the brain is doing the important things to leave them in suregrey
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13
Q

Can also do intracranaial recordings using EcOg In humans which

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places grids of electrodes

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14
Q

ECoG stands for

A

electrocorticography

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15
Q

ECoG is suitable for

A

epileptic patients

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16
Q

Diagram of ECoG electrodes placed ontop of patient’s brain

A
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17
Q

Grids in ECoG is useful for in epileptic patients

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Helping to map out different regions that are involved in seziures (to be removed surgically) or those that are not (to not be removed surgically - RED, YELLOW & GREEN)

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18
Q

Advantages of intracranial recordings (2)

A
  • Amazing spatial (mms) and temporal (msecs) resolution
  • Can assess frequency, connectivity and necessity
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19
Q

Disadvantages of intracranial recordings (4)

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  • Invasive and rare opportunities to do
  • Cannot do in neurotypical humans (and don’t know effects of existing conditions)
  • Cannot do many trials/tasks if not clinically useful
  • Typically lack coverage of brain
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20
Q

Alternative to incranaial recordings is to…

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assess same thing outside of the skull… (EEG/MEG)

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21
Q

EEG stands for

A

electroencephalography

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22
Q

Electro in EEG means

A

Electrical

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23
Q

encephalo in EEG means

A

relating to the brain

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24
Q

graphy in EEG means

A

measurement

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25
Q

EEG meausres the

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electrical activity in the brain

26
Q

Origins of EEG can be traced to

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Hans Berger

27
Q

EEG Origins

A neurologist, Hans Berger first recorded

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electrical activity on sclap in 1923

28
Q

Hans Berger’s recording of electrical activity on scalp (shown below) took

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decade for it to be taken seriously due to his views on telepathy

29
Q

Hans thought these ‘brainwaves’ emanating from the brain

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supported telepathy –> brain waves recorded could leave and be picked up and influence someone else’s brain

30
Q

EEG measures the activity of population of neurons

A

firing together

31
Q

The population of neurons firing together in EEG need to be all lined in the same ….. and need to be active.. for that activity to be picked up in the surface of scalp - (2)

A

same orientation
active simultaneously

32
Q

EEG does not look at transient (temporary) action potentials but the .. because… - (2)

A

electrical activity in pyramidal cells
Because need many synapses to be active simultaneously (1 million) i.e., synchronised neural actvitiy over several mm squared

33
Q

Why does EEG not look at action potentials?

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Action potentials are really quick and not on (active) at the same time so wouldn’t be able to see it at the surface of scalp

34
Q

Why does EEG specifically look at pyramidal cells? - (3)

A
  • Have positive charges on one side and negative charges on another side
  • All lined up on the cortical surface at the same orientaiton
  • Electrical potentials of cells add up and seeing bigger effect of many of these cells as makes it all the way outside of head
35
Q

Many pyramidal cells line up next to each other near the cortex creating a - (2)

A

dipole (tiny battery turning on and off)
Two poles of positive and negative charges

36
Q

In EEG, they are specifically measuring the populations of pyramidal neurons firing together which produces a … but its very small, typically… - (2)

A

change in electrical polarisation, large enough to be detected outside the head

tens of microvolts (micrvolts is a millionth of a volt, less than what a battery produces)

37
Q

What does this headplot show? - (6)

A

Triangle = nose
Circle = EEG electrode
Colour shows correlation between electrodes
All red ones are pos correlated with each other
All blue ones are negatively correlated with red ones

Shows = nearby electrodes are often highly correlated with each other

38
Q

Why does EEG have poor spatial resolution? (in cms) - (3)

A
  • Electric signals disperse from the source and get weaker fruther away
  • They must pass through lots of tissue (including the skull) before you can measure them, which all effect electrical current differently
  • Makes it harder to know where the signal came from
39
Q

There is a difference between source and sensor

A

space

40
Q

There are sources of activity within the

Different values obtained for different - (2)

A

brain (source space) which can be measured in fMRI reliably

Different values obtained for different parts of brain

41
Q

EEG the activity is measured at locations on

A

the scalp (sensor space)

42
Q

Can try and workout the sources of activity at sensors (e.g., mathematically) but it is

A

hard/unreliable

43
Q

Limtiation of EEG is that it misses deep sources - (3)

A
  • EEG is measured further away than intracortical recordings (e.g., ECog and depth electrode) so it is weaker signal
  • It is even worse for deep source and miss it completely
  • EEG is likely to miss deepth sources (e.g., subcortical areas, hippocampus etc..)
44
Q

Would ECoG measure deep sources in brain and is it better than EEG? - (2)

A

ECoG would also do worse for deeper sources as it is on the surface

Better than EEG

45
Q

Does depth electrode do worse for measuring deep sources in the brain?

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depth electrode would not, it would record signal from close to wherever it was placed

46
Q

EEG setup - (4)

A
  • Electrodes made up of sliver/sliver chloride and some compatible for MRI or MEG
  • A conductive gel or poaste on electrodes so can get good electrical contact with scalp
  • Electrode caps of different size to get good signal
  • Additional electrodes often place to monitor blinks and eye movement (EOG) - either subtracted out
47
Q

In EEG we want to check that impedance (measured automatically by EEG) is below … so we get good condutance

A

5kΩ (Ohms)

48
Q

in EEG , if you don’t move the hair out of the way, clean the scalp or apply the gel or don’t apply electrode firmly you can get

A

impedance (resistance) = opposite of condutance

49
Q

EEG measures the difference in electrcial charge called

A

voltage or potential difference

50
Q

It does not make sense to talk about the voltage at particular point and instead voltages are relative measures

A

across the head

51
Q

in EEG there always must be a reference electrode that is located at the

A

behind one ear or both ears

52
Q

There are many standard referencing systems to determine electrode placement which allows

A

Allows comparison across studies/labs and replication

53
Q

The most common electorde placement is the (Extended)

A

10-20 system where they place electrodes in specific places and have names for each one

54
Q

The 10-20 system works on the

A

proportion of size of your head depending on 2 reference points

55
Q

The 2 reference points 10-20 system uses- (2)

A
  • Nasion (just above the bridge of the nose)
  • The inion (bump at the base of the skull)
56
Q

Extended 10-20 system shows - (2)

A
  • Letters which give general area/lobe (e.g., Fp - prefrontal, f - frontal)
  • Numbers (or z) give left or right dimension (e.g,, z = zero, even numbers = right, odd = left)
57
Q

EEG setup Continued…

You have electrodes placed firmly on scalp cap with gel and each electrodes records the voltage that is passed through the wires to an

A

amplifier

58
Q

Why is EEG amplifier used? - (2)

A

Because the voltages measured in EEG are so small, we need to amplify them

Modern amplifiers also digitise the EEG signals and send them to a computer

59
Q

Can see EEG recording in real time in experiment as shown below:

A
60
Q

From EEG recordings (voltage over time , each electrode), you can get - (2)

A
  • EEG traces (including ERPs) which asks when there are changes in electrical activity
  • Contour/head plots (topgraphy) - asks approx where there are changes in electrical activity in sensor space
61
Q

There is also clinical applications of EEG as used in many clinical conditions such as (6)

A
  • Diagnosing and monitoring epilsey
  • Migraine
  • Movement disorders (e.g., Parkinson’s)
  • Psychiatric disorders
  • Diagnosing coma and brain death
  • Assess sleep disorders and in sleep research
62
Q

The different stages of sleep are associated with characteristic

A

patterns of EEG activity

Principles of CN Proper (19 decks)

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