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Cognitive Neuroscience > 5. Brain Imaging > Flashcards

5. Brain Imaging Flashcards

1
Q

fMRI better … resolution?

MEG/EEG better …resolution?

A

fMRI has better spatial resolution

MEG/EEG has better temporal resolution

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2
Q

why is EEG temporally highly sensitive?

A

electromagnetic waves propagate almost simultaneously

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3
Q

wat are 2 disadvantages of EEG?

solution?

A

EEG:

  1. is sensitive to neurons near skull, but deep
  2. electrical activity is distorted by tissue (skull, CSF etc)

possible solution: Electrocorticography

> record electrival activity directly from cortex surface

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4
Q

how to read an EEG

A

by Fourier transformation:

> transform complex waves into underlying sin/cosin waves

> count

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5
Q

MEG:

  1. temporal resolution?
  2. spatial resolution?

two advantages?

A

MEG:

  1. temporal resolution: milliseconds
  2. spatial resolution: few millimeters (beter than EEG)

by using magnetic source imaging

  1. entirely silent
  2. non invasive
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6
Q

what is a key difference in measurement between MRI and EEG/MEG?

A

EEG/MEG measures electrical/magnetic changes in neural activity directly

MRI measures indirectly the changes in bloodflow due to neural activity

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7
Q

wat is BOLD?

A

BOLD

> Blood Oxygen Dependent Activity

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8
Q

3 changes in blood oxygen levels due to neural activity

A
  1. blood oxygen levels drop due to consumption of oxygen
  2. overshoot of blood oxygen levels, oxygen rich blood is transported to that region
  3. blood oxygen levels go back to baseline
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9
Q

why do most of the research combine multiple measuring intruments?

A

it is not possible to get a good spatial AND temporal resolution using only one instrument

good spatial: fMRI, PET

good temporal: EEG/MEG, single cell recordings

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10
Q

wat is “co-registration”?

A

combining functional and structural imaging

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11
Q

fMRI: what is a disadvantage of subtracting conditions?

A

subtracting conditions: subtract baseline measurement from experimental measurement

disadvantage: if there is important brain activity occuring in both measurements, this data is lost

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12
Q

fMRI: what is an alternative to the subtracting conditions method?

A

parametric variation:

> gradually increase experimental task

> observe: does neural activity increase gradually as well?

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13
Q

“the resting brain is not silent”

> what does that mean?

> implications for fMRI measurements?

A

“the resting brain is not silent”

> in baseline conditions, where participants are told not to do something (e.g. speak), the brain still is active (e.g. inner speech)

> creating a valid baseline condition in fMRI research is difficult but important

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14
Q

what is DTI?

A

DTI: diffusion tensor imaging

> is a MRI method using water flow in the white matter to measure relative directions of white matter tracts

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15
Q

what is binocular rivalry?

A

binocular rivalry

> only one visual stream of input (left or right eye) is conscious at any time

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16
Q

3 main characteristics of MEG/EEG

A

MEG/EEG

  1. measures simultaneous activation of large populations of neurons
  2. this populations of neurons must have same orientation
  3. is sensitive to gradual changes in synaptic potentials
17
Q

gamma activity in the brain is indication of what?

A

gamma activity

> is a signal for exchange between cortical and subcortical regions

18
Q

what is “coding by synchrony”?

A

coding by synchrony

> random spiking of two neurons can be synchronized by an inhibitory cell

> by then firing at the same rate, they can activate a downstream cell

19
Q

MEG measures magnetic fields where?

A

MEG measures in sulci

> only there the magnetic fields can be measured

20
Q

3 steps of TMS

A

TMS

  1. coils change of current, creating a magnetic field
  2. magnetic field induces current in nearby neuron
  3. current disrupts cognitive function

> temporal lesion

21
Q

MEG

> what is the difference between a

  1. tangential dipole

and a

  1. radial dipole
A

MEG

tangential dipole: magnetic field leaves and re-enters head

radial dipole: electric current direction “leaves” head

22
Q

what are the advantages/disadvantages of TMS?

(4)

A

TMS

  1. is temporary - no brain reorganization takes place
  2. its reversible
  3. effects are focal (ca. 1cm), but it cant stimulate deep regions
  4. it can investigate the time course of cognition

(effects are brief)

23
Q

which brain property uses

  1. EEG
  2. single cell recordings
  3. TMS
  4. MEG
  5. PET
  6. fMRI
A
  1. EEG - electrical
  2. single cell recordings - electrical
  3. TMS - electromagnetic
  4. MEG - magnetic
  5. PET - hemodynamic
  6. fMRI - hemodynamic
24
Q

MRI:

what is T2?

what is T1?

A

MRI

T2: time it takes for protons to lose phase coherence

> transverse relaxation (spin-spin)

T1: time it takes for protons to realigne to magnetic field

> longitudinal relaxation (spin-lattice)

25
Q

MRI

T1 used for?

T2 used for?

A

MRI

T1 is used for structural imaging

T2 is used for functional imaging

26
Q

wat is T2*?

A

T2* is T2 + dephasing due to local inhomogeneity

27
Q

BOLD:

what kind of blood has what magnetic property?

> implications for T2 intensity?

A

high oxygen blood: not magnetic

low oxygen blood: slightly magnetic

> low oxygen blod has less T2 intensity

28
Q

fMRI: when is a brain regions active?

A

“activation” is always a statistical decision

> threshold has to be set

Cognitive Neuroscience (12 decks)

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