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530: Data Acquisition > Chapter 12 p. 2 (fMRI) > Flashcards

Chapter 12 p. 2 (fMRI) Flashcards

1
Q

neurovascular coupling is the phenomenon whereby changes in __ are modulated by changes in __

A

neural activity; vascular parameters controlling blood delivery to the brain

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2
Q

in response to local neuronal activity, __ ( a type of __) mediate changes in __, leading to enlargements of __ and increased delivery of __

A

astrocytes; glial cells; blood vessel diameter; arterioles; glucose to neurons

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3
Q

__ (especially __) also have a substantial effect upon neurovascular coupling

A

neurotransmitters; dopamine

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4
Q

dopamine terminals are found next to small intracortical arterioles and capillaries in physical adjacency to __, which are __ cells able to __ capillaries and thereby to influence __

A

pericytes; contractile; constrict or to dilate; local flow patterns

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5
Q

blood contains __ (2)

A

oxygenated hemoglobin (Hb) and deoxygenated hemoglobin (dHb)

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6
Q

Hb is __ and has __

A

diamagnetic; no magnetic moment

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7
Q

dHb is __ and has __

A

paramagnetic; magnetic moment

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8
Q

concentrations of Hb and dHb affect the __ in the brain and cause changes in the __ of brain tissue

A

local magnetic field; local relaxation constants

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9
Q

as the percentage of Hb in the blood increases, the __ increases, so that the __ goes down

A

transverse relaxation time; transverse relaxivity (1/T2)

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10
Q

as paramagnetic substances __ the local magnetic field, spins precess at __ and thus lead to __ of the transverse magnetization

A

distort; different frequencies; more rapid decay

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11
Q

__ is essentially unaffected by the percentage of oxygenated blood because it is predicated on __

A

T1 recovery; spin-lattice interactions

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12
Q

following neuronal stimulation, the concentration of dHb __ at stimulus onset (__ at 2 seconds), and then __ at 6 seconds after onset, then returns to baseline at about 10 seconds

A

increases rapidly; peaking; declines to a minimum

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13
Q

Hb concentrations begin to __ shortly after stimulus and __ after 5 seconds, with a __ at 10 seconds

A

rise; peak; slow decline

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14
Q

the changes in d/Hb after stimulation is due to the fact that active neurons utilize __ to support their initial activity, so the initial metabolic response of neurons is __

A

whatever oxygen is already present; oxidative

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15
Q

neuronal activity may lead to prolonged reductions in __ compared with flow, and these changes persist even __

A

glucose metabolism; after activity ceases

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16
Q

under normal conditions, Hb is converted to dHb __

A

at a constant rate within the capillary bed

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17
Q

when neurons become active, the vascular system supplies __

A

more Hb than is needed by the neurons through an overcompensatory increase in blood flow

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18
Q

the overcompensatory increase in blood flow results in an increase in the amount of __ and a corresponding decrease in __, leading to a __ fMRI image

A

dHb; signal loss due to T2* effects; brighter

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19
Q

the BOLD signal contrast occurs not because __ but rather because __

A

Hb increase the MR signal; Hb displaces dHb which had been suppressing MR signal intensity prior to neuronal activation

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20
Q

after a single exogenously-triggered neuronal activation, the BOLD response exhibits __

A

a characteristic rise and fall followed by an undershoot and return to baseline

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21
Q

the shape of the BOLD response varies with the __ and the classical BOLD response may have a different __ depending on __

A

nature of the stimulus; temporal profile; activation pattern

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22
Q

after a block of successive event-related activations, the BOLD response changes shape by __

A

developing a plateau instead of a peak

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23
Q

the length of the BOLD plateau is proportional to the __, as well as the __

A

number of events which trigger the neuronal activation; frequency of these events

24
Q

to appropriately model the BOLD response after a complex stimulus, __ is often required

A

complex mathematical modeling of the response itself

25
Q

cerebral blood flow (CBF) indicates the amount of __

A

blood supply to the brain within a specified period of time

26
Q

cerebral blood volume (CBV) indicates the amount of __

A

blood which is present at any given time within a specified brain tissue volume

27
Q

the BOLD signal depends not only on the rate of __ but also on __ and __ levels

A

oxygen extraction; CBF; CBV

28
Q

after stimulus offset, __ levels return quickly to baseline levels but __ levels off more slowly

A

CBF; CBV

29
Q

elevated CBV relative to CBF causes an increase in __ in the tissue, which is probably the cause of the __ in the BOLD signal

A

total amount of dHb present; post-stimulus undershoot

30
Q

simultaneous ECoG and fMRI recordings indicate the relationship between __ (4)

A

BOLD response, local field potentials (LFPs), multi-unit activity (MUA), and single-unit activity (SUA)

31
Q

SUA is due to the __

A

firing of individual neurons close to recording electrodes

32
Q

MUA is due to the __

A

collective firing of large PY neurons within a few hundred microns of the ECoG electrodes

33
Q

LFPs are __

A

synchronous changes in integrative activity from cells within a few mm of the electrode

34
Q

the longer the stimulus, the more sustained the __ (4) are, though the neural response always __

A

SUA, MUA, LFP, and BOLD responses; precedes the BOLD response, which is much slower

35
Q

even in cases where cells in neural tissue are activated by a very precise and well-defined stimulus, there remains __

A

substantial variability in the amplitude and form of the hemodynamic response across events

36
Q

these individuals events must be averaged in order to retrieve __ and to increase the __ of the experiment

A

the ‘classical’ shape of the BOLD response; SNR

37
Q

generally, single-trial fMRI data do not provide __, so __ must be employed instead

A

a sufficiently accurate basis for interpretation and analysis; multi-trial paradigms

38
Q

__ noise factors make the true BOLD response __

A

intrinsic and extrinsic; very difficult to isolate from single-trial experiments

39
Q

the functional resolution of fMRI is strongly dependent upon the __

A

concordance of neuronal activity and vascular responses to that activity

40
Q

the maps of neuronal activations generated using __ do not overlap very well with those create via __

A

electrophysiological methods; fMRI

41
Q

the size of activation maps is larger when measured via __ than via __

A

fMRI; ECoG

42
Q

spatial filtering effects of the vascular system cause the fMRI signal to be __

A

spatially blurred over a larger spatial extent than ECoG signals

43
Q

because the typical fMRI voxel size is larger than ideal, __ are often encountered because decreasing voxel size results in reduced __ and increased __

A

partial volume effects; SNR; acquisition time

44
Q

the BOLD signal is due to __, which are present in __ and __ but not in __

A

dHb levels; capillaries; veins; arterial blood

45
Q

dHb molecules are __ and generate __ which unfortunately extend __

A

paramagnetic; magnetic field changes; far into surrounding tissue

46
Q

the primary mechanism of the BOLD signal is the __ within __ molecules as these molecules diffuse through __

A

dephasing of spins; water; these gradient fields

47
Q

spins located within __ give rise to the __ of the BOLD signal, while spins in __ (__) give rise to the __ of the signal

A

vessels; intravascular component; surrounding tissues (parenchyma); extravascular components

48
Q

both intravascular and extravascular components originate in __, which are very __ and __. thus, the absolute limit for measuring hemodynamic activity is the average __ and this cannot be __

A

capillaries; small in diameter; close together; separation between capillaries; improved

49
Q

as brain activations are elicited, __ blood enters the venous system and displaces __, thus __ BOLD signals __ from active neurons

A

Hb-rich; dB; increasing; downstream

50
Q

some of the BOLD response can be due to __, not to neuronal activation, a phenomenon known as __

A

venous drainage; the large vessel effect

51
Q

sequences have been designed to attenuate the large vessel effect by exploiting the fact that the magnetic field due to __ changes __ over space as it extends into __. for this reason, nearby __ spins within diffusing water experience relatively __ as they move

A

dHb in large vessels; slowly; surrounding tissues and fluid; extravascular; small B field changes

52
Q

SE sequences can reverse the loss of phase coherence due to __ but not due to __ because the latter generate __ B field gradients and the lost phase coherence cannot be completely refocused by __

A

large vessels; small vessels; large; 180 degree SE rephasing pulses

53
Q

the TR has a very strong effect upon the __ of fMRI signals, particularly because the __ are difficult to resolve with __ sampling, which makes modeling the fMRI signal difficult if the stimuli have a complex time profile

A

time resolution; initial and final undershoots; low-frequency

54
Q

when more than one stimulus is presented within a short period of time, it leads to __

A

an overlap of BOLD signals

55
Q

generally, the response due to two distinct stimuli is the __ (i.e. the BOLD response has the property of __)

A

sum of the individual responses due to each stimulus; linearity

56
Q

if stimuli are presented very closely together, the combined response may not be __ and we may notice, in fact, a __ due to the so-called __

A

additive; reduction in hemodynamic amplitude; BOLD refractory effect

530: Data Acquisition (13 decks)

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