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BMS 248 - Neural circuits > Modern methods in neuroscience I > Flashcards

Modern methods in neuroscience I Flashcards

1
Q

What is magnetic resonance imaging used for?

A

To produce high resolution images of under the skin

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2
Q

Why is MRI safer than X-rays and CT scans?

A

Doesn’t use ionising radiation

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3
Q

What does MRI scanning use to get an image of under the skin?

How?

A

Powerful magnets

Elicit a signal from the protons contained in the water molecules of the body

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4
Q

What type of particle emits electromagnetic waves?

What does this produce?

A

An ACCELERATING, CHARGED particle

Produces electromagnetic radiation which can be detected

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5
Q

What is acceleration?

A

The rate of CHANGE of velocity

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6
Q

What does velocity comprise of?

A

Magnitude(size) AND direction

How FAST something moves in a particular DIRECTION

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7
Q

If a particle is accelerating, what has changed?

A

The magnitude or direction of a CHARGED particle

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8
Q

What type of particle is CONSTANTLY accelerating?

What does this particle release?

A

A spinning CHARGED particle - A PROTON

Constantly releases electromagnetic radiation

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9
Q

What does any spinning particle have?

A

A magnetic dipole (North and South)

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10
Q

How are the protons arranged in a given body tissue?

What does this cause?

A

All the north poles are orientated in DIFFERENT directions

Cancel each other out
Causes NO NET magnetic effect
NO electromagnetic radiation can be detected (it is 0)

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11
Q

What happens when a powerful VERTICAL, STATIC external magnetic field is applied?

What does this produce?

A

Protons line up with the magnetic field (vertically) - no longer cancel each other out

Forms a weak electromagnetic field in the tissue
All the spins of the protons add together - produces electromagnetic radiation

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12
Q

What happens when a powerful HORIZONTAL, PULSING external magnetic field is applied? (after the vertical one)

What does this produce? Why?

A

Pushes the protons over, causing them to wobble on their axis

Produces a VARYING, DETECTABLE magnetic field
As change in direction - acceleration in the the change in velocity (magnitude/direction)

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13
Q

What is radio frequency?

When is this used?

A

Magnetic field that is rapidly pulsed on and off

Used as a horizontal magnetic field to push the protons over on their axis

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14
Q

What does precess mean?

When is this achieved?

A

When the protons wobble on their axis

Occurs when there is a vertical static magnetic field and a horizontal radio frequency

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15
Q

What component of the magnetic field of the protons is easier to detect? Why?

A

The horizontal component - gets bigger and smaller as the protons are knocked over

Changes the magnetic field

Easier to measure change

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16
Q

In a MRI machine, what causes the vertical magnetic field?

A

Super-cooled, super-conducting coil

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17
Q

In a MRI machine, what causes the horizontal magnetic field?

What is this magnetic field also called?

A

The head coil

RF - radio frequeny

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18
Q

Which magnetic field is static?

A

Vertical

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19
Q

What happens to the protons when the RF is turned off?

A

Protons move out of phase - Dephase

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20
Q

How does dephasing occur?

A

Quickly

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21
Q

What does dephasing lead to?

A

A loss of horiztonal magnetisation and a weakened signal in the horizontal field - The ‘dephasing signal’

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22
Q

What is T2?

A

The time constant of the weakening horizontal field

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23
Q

What is a T2 weighted image based upon?

A

The dephasing part of the cycle

24
Q

What happens to the protons if the horizontal radio frequency pulse remains off?

What does this result in?

A

Protons realign themselves with the strong VERTICAL magnetic field

Resulting in the restoration of the vertical magnetisation
Increase in the vertical signal

25
Q

Does the realignment happen faster or slower than the dephasing phase?

A

Much slower

26
Q

How is the return to the original alignment of the protons measured?

A

Indirectly

27
Q

What is T1?

A

The time constant of the recovery of the longitudinal magnetisation

28
Q

What is a T1 weighted image based upon?

A

When all the protons are aligned in the vertical plane (no horizontal magnetic field)

29
Q

When is the signal in T2 strongest?

When does this signal reduce?

A

When the protons are in phase

Reduces when the protons dephase

30
Q

When is the signal in T1 weakest?

When does this signal increase?

A

When the protons are horizontal

Increases when the protons stand up and realign with the vertical field

31
Q

What is useful in getting information about the tissue the protons are in?

A

Changes

Especially in the RATE OF CHANGE of the signal strength

32
Q

What do the values of T1 (realignment) and T2(dephasing) of the protons depend upon?

A

The surrounding matter

33
Q

How quick do protons dephase and realign in DENSE tissue? (eg. bone)

Why?

A

Quicker than if in a less dense tissue

Because the protons are closer together

34
Q

What is used to construct an MRI image?

A

A computer system attached to the scanner, which assigns a particular brightness value to the various T1 and T2s measured

35
Q

In T2, what colour do dense substances appear?

A

Bright

36
Q

In T1, what colour do dense substances appear?

A

Black

37
Q

What is the point in having T1 and T2 images?

A

Can easily see different structures

Which one is used depends upon what the researcher wants to visualise

38
Q

What information does MRI give?

A

Structural information

39
Q

What can be used to determine what parts of the brain is functioning in different tasks?

A

fMRI

functional magnetic resonance imaging

40
Q

What is fMRI and what is it used for?

A

Functional MRI

Used to determine what parts of the brain are functional during different tasks

41
Q

What did James Williams do?

What did this show?

A

Placed a subject on a balanced table that could tip downwards at the head or foot, if the weight at either end was increased

  • Showed that if emotional/intellectual activity began in the subject - the head end went down
  • As a result of blood rush
42
Q

What happens to the blood in the brain?

A

Blood flow SLOWLY increases to metabolically active areas of the brain

43
Q

What do some people suggest about the blood flow to metabolically active parts of the brain?

A

Suggest it is to supply area working hard with nutrients and oxygen
And to flush away the metabolic byproducts

44
Q

What does oxygenated blood do in the brain?

What happens after this

A

Enters the capillary bed supplying an area of metabolically active brain

Tissue then extracts the O2 from the blood

Deoxygenated blood leaves the capillary bed

45
Q

Is oxygenated or deoxygenated blood paramagentic (has magnetic properties??

What does this allow?

A

Deoxygenated blood

Magnetic field of the deoxygenated blood can be detected in an MRI scanner

Can see the difference between oxygenated and deoxygented blood on the MRI image

46
Q

What is a ‘BOLD’ signal?

A

Blood Dependant Oxygenation Level Dependant signal

47
Q

If there is more deoxygenated blood present, what happens to the signal?

A

It is brighter

48
Q

If there is more deoxygenated blood coming out of a specific brain area, what is the assumption?

A

That more oxygenated blood has travelled to that area of the brain

So, that part of the brain is more active

49
Q

What do computer programmes such as ‘Statistical Parametric Mapping’ and ‘FSL’ do?

How do they do this?

What does this ‘map out’

A

Calculate the probability that a small chunk of brain has a DIFFERENT BOLD signal to the one next to it (Probability of increased blood flow to that tiny area)

  • Compare the voxel of one brain area to the voxel of the neighbouring area using a t-test
  • Assign a colour to each probability
  • Overlay the colours on the ANATOMICAL MRI image

Maps out activation of the brain

50
Q

What is a VOXEL?

A

A 3D pixel (volumetric pixel)

Cube shaped pixel of the brain

51
Q

Why is the nature of the BOLD signal controversial?

Why?

A

Some think it is may be a non-specific ‘cooling system’ of the brain

Because the increased blood flow to the brain area FAR EXCEEDS the requirements of the active neurons

52
Q

Why is the usefulness of fMRI in question?

A
  • Patterns of activation can be DIFFERENT in different patients performing the SAME task
53
Q

How can you make comparisons between the fMRI of different people?

What are the disadvantages of this?

A

Apply non-linear registration to a STANDARD template

Disadvantages:

  • Produces an average picture of the brain which distorts the original image and makes it appear fuzzy
  • As each brain is different
54
Q

What is fMRI good and bad for?

A

Good at telling you WHERE the brain is activated (good spatial resolution)

Bad at telling you WHEN the brain is activated (bad temporal resolution)

55
Q

Why does fMRI have poor temporal resolution?

A

It takes several seconds for the arterioles to dilate and allow increased blood flow (detected in fMRI)

BOLD signal takes several seconds to build up

56
Q

What is fMRI not idea for?

Example?

A

Experiments in which timing is important

Eg. investigating rapid cognitive tasks

57
Q

If investigating tasks where timing is important, what must fMRI be coupled with?

How is this technique different to fMRI?

A

ELECTROENCEPHALOGRAPHY:

  • High TEMPORAL resolution
  • Low SPATIAL resolution

BMS 248 - Neural circuits (16 decks)

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