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PHGY314 > Functional imaging of resting state > Flashcards

Functional imaging of resting state Flashcards

1
Q

how many coils does an MRI scanner have?

A

Main coil, RF coil, and 3 gradient coils

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2
Q

why can CBF (cerebral blood flow) indicate brain activity?

A

due to neurovascular coupling, a complex biological transformation

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3
Q

what is a voxel?

A

a 3D pixel

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4
Q

what is PET?

A

a physical measure via changes in blood vessels

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5
Q

what is NIRS OI?

A

near infrared spectrometry optical imaging: measure of the hemodynamic signal

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6
Q

what is the formula to graph the CBF change according to the stimulus in fMRI?

A

T2*/T2/CBF

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7
Q

fMRI is an indirect measure of what?

A

neuronal activity

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8
Q

MRI/PET/NIRS OI measurement allow for what?

A

imaging of changes in blood vessels in the brain

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9
Q

how are intra-cellular recordings taken? 2 ways

A
  1. intra-cellular: electrode in the axon measure potential inside axon and compares with the potential outside = membrane potential
  2. patch clamp: a micropipette merges with the membrane of a neuron cell body, putting and electrode inside and measure potential inside vs outside
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10
Q

ECM acts a a volume conductor for neurons thanks to what?

A

the ions in it that conduct electrical signal

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11
Q

what do Kirchhoff’s laws say about how neurons ensure they don’t loose charges?

A

when a neuron has different membrane potential at different regions, there is a flow of current in the neurons matched by a return current in the ECM

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12
Q

what is used in extracellular potential recordings?

A

the ECM current that matches the current inside the neurons

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13
Q

what are the 2 components of the mean EC potential?

A
  • LFP local field potential = filters out peaks above 150 Hz (it’s the input to the area)
  • MUA multi unit activity = filter out peaks under 400 Hz (it’s the output of the area)
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14
Q

extracelullar recordings are a reflection of what?

A

of the APs (of synaptic activity)

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15
Q

give the characteristic of MUA measurements

A
  • represents APs of neurons around the electrode
  • quick: lasts 1 msec
  • spatial summation radius of 100-200 microns
  • OUTPUT of cortical area
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16
Q

more precisely what do MUA represent?

A
  • projections neurons sending output to white matter
  • local intra-cortical activity
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17
Q

give the characteristics of LFP

A
  • represents all the synaptic activity
  • longer: 10-100 msecs
  • bigger: spatial summation of 1-2mm
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18
Q

more precisely what do LFP represent?

A
  • PSPs population synaptic potentials
  • Voltage-gated membrane oscillations
  • INPUT to cortical area
  • local intra-cortical activity
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19
Q

why is extracellular recording better than EEG?

A
  • better spatial resolution
  • better signal to noise ratio
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20
Q

how can LFPs be further classified?

A

into frequency bands used in EEG - delta, theta, alpha, beta, and gamma

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21
Q

how many neurons are in a 2x2x2 mm3 voxel approximately? what about synapses?

A

1 millions neurons
7.2 billions (x 10^9) synapses

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22
Q

what is BOLD signal?

A

Blood Oxygenation Level Dependent signal: reflects the content of deoxy-HB in blood vessels (hemodynamic response)

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23
Q

where is the BOLD signal coming from in the brain?

A

in the PIA matter, but some arteries penetrate the cortex from the PIA

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24
Q

BOLD signal relies on what property of hemoglobin?

A

magnetic properties

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24
Q

Deoxy-hemoglobin is ___-______

A

para-magnetic

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24
Q

fMRI detects the BOLD signals, meaning it detects what?

A

the change in magnetic field

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25
Q

what is the composition of blood vessels in the cartoon? which component changes the magnetic field?

A
  • deoxyhemoglobin & oxyhemoglobin
  • deoxyhemoglobin decreasing increases BOLD signal
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26
Q

what acts as a contrast agent?

A

deoxy-hemoglobin

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27
Q

what are called vessels that penetrate the cortex?

A

cortical blood vessels

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28
Q

name potential control sites of cerebral hemodynamic response

A

arteriolar smooth muscle, and pericytes around capillaries

29
Q

what signals is fMRI dependent on because they are dominant?

A

increased CBF and decreased deoxy-Hb are dominant over increased CBV and drive magnetic resonance signal UP

30
Q

CBF can also be referred to as what?

A

velocity

31
Q

why is there an initial dip in the BOLD curve signal before the big increase in change?

A

initial dip is due to the increase in oxygen consumptio

32
Q

why is there a dip after the BOLD curve signal after the big increase in change?

A

follow up dip is due to the increase in CBV

33
Q

What is the origin of the signal: arteries, arterioles, capillaries, venules or veins?

A

mainly capillaries, venules, and veins

34
Q

why does the main BOLD signal not come from arteries and arterioles?

A

there is almost no deoxyhemoglobin in arteries/rioles because they contain oxy-hemoglobin.
Veins push deoxy-hemoglobin out towards the lungs to be oxygenated.

35
Q

what is optical imaging of intrinsic signals based on?

A

the fact that deoxy-Hb has a way higher light absorption value than oxy-Hb at 605 nm

36
Q

what’s the difference between deoxy-Hb and oxy-Hb magnetic properties?

A

deoxy-Hb is paramagnetic (STRONG magnet)
oxy-Hb is diamagnetic (Weak magnet)

37
Q

what is optical imaging of Voltage Sensitive Dyes?

A

compound is applied to the brain and binds neuronal membranes, and fluorescence when there is a change in membrane potential

38
Q

how accurate are voltage sensitive dyes?

A

very! give the same results as intracellular recordings

39
Q

Voltage-Sensitive Dyes are capable of providing linear measurements of firing activity of what?

A

of single neurons OR of large neuronal populations

40
Q

what level of light (nm) must be used to excited voltage sensitive dye and deoxy/oxy-Hb? (in prof’s experiement)

A

630 nm

41
Q

how many nm is the voltage sensitive dye fluorescence?

A

690 nm

42
Q

when measuring BOLD signal via optical imaging and neurophysiology using voltage-sensitive dyes, what can we see?

A
  • BOLD lags behind neurophysiological response
43
Q

why does BOLD lag behind neurophysiologic response of voltage-sensitive dye?

A

voltage sensitive dye reacts directly in the grey matter at the same time of the stimulus because it does not need to “wait” for the blood vessel to respond

44
Q

Which type of neuronal activity is reflected in fMRI
signals: spikes vs. synaptic activity?

A

based on experiment comparing BOLD signal to monkey spiking activity, it reflects SPIKES of activity.
BUT this doesn’t answer it

45
Q

what did they find when measuring CBF versus LFP during climbing fiber vs parallel fiber stimulation?

A
  • linear relationship in climbing fibers (CBF is proportional to LFP)
  • non linear sigmoidal relationship in parallel fibers
46
Q

they wanted to know if fMRI BOLD signal was caused by spikes (APs) or synaptic activity. how did they test that? what was the result?

A

block APs in the cerebellum; found that CBF increased, therefore CBF is independent of spiking

47
Q

BOLD response was showed to be linear with what, spikes or synaptic activity?

A

BOTH (MUA and LFP)

48
Q

what did they find when looking at the duration of MUA vs LFP compared to the BOLD signal after a stimulus?

A

MUA & SDF did not have the same duration;
LFP had the same duration

49
Q

what is SDF?

A

spike density function (AP measurement)

50
Q

why is neurophysiological response more reliable than BOLD fMRI response?

A

it has a higher signal-to-noise ration

51
Q

describe the spontaneous fluctuations of BOLD signals observed in human brain

A

large amplitude fluctuations that are slow (0.01-0.1Hz aka 10s per cycle)

52
Q

in what areas were similar fluctuations found?

A

somato cortixes, putamin, thalamus, cerebellum

53
Q

what is structural/anatomical connectivity?

A

axonal projections between two areas

54
Q

what is functional connectivity?

A

statistical dependence between time-course of activities in two areas

55
Q

what is the talairach coordinate system?

A

aligning brain by rotating the brain such that the anterior and posterior commissures crossings with the midsagittal plane form a horizontal line

56
Q

what is the 0, 0, 0 point in the talairach coordinate system?

A

the anterior commissure

57
Q

what is the default mode network?

A

brain regions whose CBF (activity) decrease during attention

58
Q

default mode networks is hypothesized to have what functions?

A
  • supports self referential processes
  • introspection
  • mentalization, imagination to fill social void in loneliness
  • consciousness and awareness
59
Q

in what situations is the default mode networks activity altered?

A

during sleep and in mild cognitive impairment, Alzheimer’s disease, schizophrenia, depression

60
Q

What can spontaneous activity and resting state
networks be used for? (3)

A
  • analyzing connection patterns
  • diagnosing neurological and psychiatric conditions
  • serving as biomarkers for progression of diseases and testing drugs
61
Q

what is macroscale? give example

A

lower spatial resolution studies: brain regions and inter-regional pathways
- fMRI, EEG/MEG

62
Q

what is microscopic scale?

A

Single neurons and their synaptic connections

63
Q

what is meso-scopic scale?

A

Connections within and between cortical columns or other types of local cell assemblies

64
Q

intra-cellular provide _____ recordings of activity than fMRI

A

faster

65
Q

how is the correlation between intra-cellular recordings and voltage-sensitive dyes recordings?

A

high: 0.9 pearson’s correlation

66
Q

intra-cellular recordings measure what?

A

membrane potential

67
Q

why is it thought that LFP and voltage-sensitive dyes show more what than what? why?

A

they show more membrane potential and APs because the surface of dendrites and cell body is way bigger than the axon’s

68
Q

do the brain’s functional architectures during activation and rest that correspond at macro-scale also correspond at meso-scale?

A

yes

69
Q

how did they test if the brain’s functional architectures during activation and rest that correspond at macro-scale also correspond at meso-scale?

A

compared meso-scale orientation maps when attentive to grating stimulus vs spontaneous activity maps of the same neurons

70
Q

what control did they use when testing that the correlation between the meso-scale maps were not due to chance?

A

inverted the image of the evoked map

71
Q

do the brain’s functional architectures during activation and rest that correspond at macro-scale also correspond at micro-scale (APs)?

A

yes: neurons have more chance to fire when the spontaneous pattern is similar to the evoked pattern

PHGY314 (9 decks)

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