Functional imaging of resting state Flashcards
how many coils does an MRI scanner have?
Main coil, RF coil, and 3 gradient coils
why can CBF (cerebral blood flow) indicate brain activity?
due to neurovascular coupling, a complex biological transformation
what is a voxel?
a 3D pixel
what is PET?
a physical measure via changes in blood vessels
what is NIRS OI?
near infrared spectrometry optical imaging: measure of the hemodynamic signal
what is the formula to graph the CBF change according to the stimulus in fMRI?
T2*/T2/CBF
fMRI is an indirect measure of what?
neuronal activity
MRI/PET/NIRS OI measurement allow for what?
imaging of changes in blood vessels in the brain
how are intra-cellular recordings taken? 2 ways
- intra-cellular: electrode in the axon measure potential inside axon and compares with the potential outside = membrane potential
- patch clamp: a micropipette merges with the membrane of a neuron cell body, putting and electrode inside and measure potential inside vs outside
ECM acts a a volume conductor for neurons thanks to what?
the ions in it that conduct electrical signal
what do Kirchhoff’s laws say about how neurons ensure they don’t loose charges?
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
what is used in extracellular potential recordings?
the ECM current that matches the current inside the neurons
what are the 2 components of the mean EC potential?
- 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)
extracelullar recordings are a reflection of what?
of the APs (of synaptic activity)
give the characteristic of MUA measurements
- represents APs of neurons around the electrode
- quick: lasts 1 msec
- spatial summation radius of 100-200 microns
- OUTPUT of cortical area
more precisely what do MUA represent?
- projections neurons sending output to white matter
- local intra-cortical activity
give the characteristics of LFP
- represents all the synaptic activity
- longer: 10-100 msecs
- bigger: spatial summation of 1-2mm
more precisely what do LFP represent?
- PSPs population synaptic potentials
- Voltage-gated membrane oscillations
- INPUT to cortical area
- local intra-cortical activity
why is extracellular recording better than EEG?
- better spatial resolution
- better signal to noise ratio
how can LFPs be further classified?
into frequency bands used in EEG - delta, theta, alpha, beta, and gamma
how many neurons are in a 2x2x2 mm3 voxel approximately? what about synapses?
1 millions neurons
7.2 billions (x 10^9) synapses
what is BOLD signal?
Blood Oxygenation Level Dependent signal: reflects the content of deoxy-HB in blood vessels (hemodynamic response)
where is the BOLD signal coming from in the brain?
in the PIA matter, but some arteries penetrate the cortex from the PIA
BOLD signal relies on what property of hemoglobin?
magnetic properties
Deoxy-hemoglobin is ___-______
para-magnetic
fMRI detects the BOLD signals, meaning it detects what?
the change in magnetic field
what is the composition of blood vessels in the cartoon? which component changes the magnetic field?
- deoxyhemoglobin & oxyhemoglobin
- deoxyhemoglobin decreasing increases BOLD signal
what acts as a contrast agent?
deoxy-hemoglobin
what are called vessels that penetrate the cortex?
cortical blood vessels
name potential control sites of cerebral hemodynamic response
arteriolar smooth muscle, and pericytes around capillaries
what signals is fMRI dependent on because they are dominant?
increased CBF and decreased deoxy-Hb are dominant over increased CBV and drive magnetic resonance signal UP
CBF can also be referred to as what?
velocity
why is there an initial dip in the BOLD curve signal before the big increase in change?
initial dip is due to the increase in oxygen consumptio
why is there a dip after the BOLD curve signal after the big increase in change?
follow up dip is due to the increase in CBV
What is the origin of the signal: arteries, arterioles, capillaries, venules or veins?
mainly capillaries, venules, and veins
why does the main BOLD signal not come from arteries and arterioles?
there is almost no deoxyhemoglobin in arteries/rioles because they contain oxy-hemoglobin.
Veins push deoxy-hemoglobin out towards the lungs to be oxygenated.
what is optical imaging of intrinsic signals based on?
the fact that deoxy-Hb has a way higher light absorption value than oxy-Hb at 605 nm
what’s the difference between deoxy-Hb and oxy-Hb magnetic properties?
deoxy-Hb is paramagnetic (STRONG magnet)
oxy-Hb is diamagnetic (Weak magnet)
what is optical imaging of Voltage Sensitive Dyes?
compound is applied to the brain and binds neuronal membranes, and fluorescence when there is a change in membrane potential
how accurate are voltage sensitive dyes?
very! give the same results as intracellular recordings
Voltage-Sensitive Dyes are capable of providing linear measurements of firing activity of what?
of single neurons OR of large neuronal populations
what level of light (nm) must be used to excited voltage sensitive dye and deoxy/oxy-Hb? (in prof’s experiement)
630 nm
how many nm is the voltage sensitive dye fluorescence?
690 nm
when measuring BOLD signal via optical imaging and neurophysiology using voltage-sensitive dyes, what can we see?
- BOLD lags behind neurophysiological response
why does BOLD lag behind neurophysiologic response of voltage-sensitive dye?
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
Which type of neuronal activity is reflected in fMRI
signals: spikes vs. synaptic activity?
based on experiment comparing BOLD signal to monkey spiking activity, it reflects SPIKES of activity.
BUT this doesn’t answer it
what did they find when measuring CBF versus LFP during climbing fiber vs parallel fiber stimulation?
- linear relationship in climbing fibers (CBF is proportional to LFP)
- non linear sigmoidal relationship in parallel fibers
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?
block APs in the cerebellum; found that CBF increased, therefore CBF is independent of spiking
BOLD response was showed to be linear with what, spikes or synaptic activity?
BOTH (MUA and LFP)
what did they find when looking at the duration of MUA vs LFP compared to the BOLD signal after a stimulus?
MUA & SDF did not have the same duration;
LFP had the same duration
what is SDF?
spike density function (AP measurement)
why is neurophysiological response more reliable than BOLD fMRI response?
it has a higher signal-to-noise ration
describe the spontaneous fluctuations of BOLD signals observed in human brain
large amplitude fluctuations that are slow (0.01-0.1Hz aka 10s per cycle)
in what areas were similar fluctuations found?
somato cortixes, putamin, thalamus, cerebellum
what is structural/anatomical connectivity?
axonal projections between two areas
what is functional connectivity?
statistical dependence between time-course of activities in two areas
what is the talairach coordinate system?
aligning brain by rotating the brain such that the anterior and posterior commissures crossings with the midsagittal plane form a horizontal line
what is the 0, 0, 0 point in the talairach coordinate system?
the anterior commissure
what is the default mode network?
brain regions whose CBF (activity) decrease during attention
default mode networks is hypothesized to have what functions?
- supports self referential processes
- introspection
- mentalization, imagination to fill social void in loneliness
- consciousness and awareness
in what situations is the default mode networks activity altered?
during sleep and in mild cognitive impairment, Alzheimer’s disease, schizophrenia, depression
What can spontaneous activity and resting state
networks be used for? (3)
- analyzing connection patterns
- diagnosing neurological and psychiatric conditions
- serving as biomarkers for progression of diseases and testing drugs
what is macroscale? give example
lower spatial resolution studies: brain regions and inter-regional pathways
- fMRI, EEG/MEG
what is microscopic scale?
Single neurons and their synaptic connections
what is meso-scopic scale?
Connections within and between cortical columns or other types of local cell assemblies
intra-cellular provide _____ recordings of activity than fMRI
faster
how is the correlation between intra-cellular recordings and voltage-sensitive dyes recordings?
high: 0.9 pearson’s correlation
intra-cellular recordings measure what?
membrane potential
why is it thought that LFP and voltage-sensitive dyes show more what than what? why?
they show more membrane potential and APs because the surface of dendrites and cell body is way bigger than the axon’s
do the brain’s functional architectures during activation and rest that correspond at macro-scale also correspond at meso-scale?
yes
how did they test if the brain’s functional architectures during activation and rest that correspond at macro-scale also correspond at meso-scale?
compared meso-scale orientation maps when attentive to grating stimulus vs spontaneous activity maps of the same neurons
what control did they use when testing that the correlation between the meso-scale maps were not due to chance?
inverted the image of the evoked map
do the brain’s functional architectures during activation and rest that correspond at macro-scale also correspond at micro-scale (APs)?
yes: neurons have more chance to fire when the spontaneous pattern is similar to the evoked pattern
