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PSYT 500 > Lecture 3 > Flashcards

Lecture 3 Flashcards

1
Q

the human brain has a mass of ____g and has ____ billion neurons

A

1500; 90

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2
Q

the cerebral cortex has:
1. ___ billion neurons (___% of all neurons)
2. ____ trillion synapses (9.5 connection/neuron)
3. _____km of white matter axons

A

16; 20-50%
150
160,000

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3
Q

the cerebellum has ___ billion neurons (___% of all neurons)

A

69; 50-80%

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4
Q

subcortical structures contain ___ billion neurons (___% of all neurons)

A

0.7; 0.8%

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5
Q

brain architecture is also known as brain ___

A

structure

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6
Q

the brain is __% of body mass

the brain consumes ___% of body energy consumption

changes in region specific activity only account for <__% of baseline activity

A

2; 20; 5

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7
Q

how does brain development relate to synaptic density?

A

looks like a log function (increases, then slowly decreases)

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8
Q

how does brain development relate to grey-matter density?

A

normalized at 15 years of age

see peaks in grey matter earlier in life (6yo), with slight decline, showing that the brain is always refining

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9
Q

which founding father of the MRI did experiments on himself?

A

Peter Mansfield

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10
Q

what are the changes in what we see using a 1) 0.1T, 2) 1.5T and 3) 7T?

A

1) general form
2) see how parts are connected (great contrast)
3) see sub-ml structure and blood vessels

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11
Q

what is the temporal/spatial resolution of 1)aMRI, 2)fMRI, 3)FDG-PET, 4)EEG/MEG?

A

1) great spatial res (sub-milimetric), bad temporal res (days/weeks)

2) OK spatial res (millimetres) and pretty good temporal res (ms-s)

3) not great spatial res (ml-cm) and OK temporal res (minutes)

4) worst spatial res (cm), best temporal res (ms)

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12
Q

how does the aMRI work?

A
  • differences in density are all product of how you manipulate water in a magnet
  • this works since the brain is mostly made up of water
  • manipulate the H atoms in the water (each have proton in nucleus) -> protons can be manipulated by the magnet
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13
Q

what are the nuclear spin systems?

A

Collection of identical nuclei (regardless of environment)

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14
Q

___% of the human body is water

____% of the human brain is water

H atoms are abundant throughout the human ____

A

57% of the human body is water

75-78% of the human brain is water

H atoms are abundant throughout the human body

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15
Q

protons in H have ___, ___ and are ____ charged

A

mass, spin positively

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16
Q

what happens when a proton is left alone?

A

wants to precess (magnetic moment), so it sits around and rotates, creating current (since its charged)

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17
Q

what is the magnetic moment vector?

A

in presence of no mag field, each magnetic moment live with no preferred direction

in field, the moments align in the direction of the field

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18
Q

explain: μ = ϒϕ

A

μ: tendency of a proton to align with magnetic field

ϒ: gyromagnetic ratio

ϕ: angular momentum

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19
Q

what is nuclear magnetism?

A

Macroscopic alignment of a spin system in the presence of a magnetic field

(once we have the alignment, can add another pulse which pushes the alignment a bit -> ask what properties occur when they try to go back in the right direction)

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20
Q

explain what happens during the application of a RF field

A

B1 is a radiofrequency field tuned to the Larmor Frequency and applied in the transverse lane (ie: x,y) plane

The bulk magnetization (M) tips away from the z-axis and towards the x,y plane (also at the Larmor Frequency)

B0 causes M to precess
around B0

The Larmor Frequency (ω0) is the frequency of the precession

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21
Q

what is the main source of signal/contrast in the mri?

A

so they start to rotate down in the x-y plane, measure how long it takes it to do that or come back

basic fundamentals to understanding how we get a signal

22
Q

why structural mri ? (3)

A

Acquisition: Detailed, Reliable and Reproducible

Analysis: Flexible and Multi-featured

Underlying biology: Dynamic rather than Static

23
Q

what is acquisition?

A

measure brain changes in response to drugs or things happening in short period of time

subtle changes detected in vivo

24
Q

who invented the mri and how many Nobel prizes were given?

A

Laterbur, Mansfield
2

25
Q

why do we use an integrated neuroscience approach?

A

think about how brain may change in response to diff functions of life

26
Q

what brain morphology can be detected in vivo?

A

tissue classification, white-matter density, deformation field, segmentation, cortical thickness, cerebral sulci

27
Q

what are caveats?

A

choice of acquisition protocol (FLASH, MPRAGE, MDEFT) -> differences in contrast

28
Q

why do we use caveats ?

A

since u manipulate water, lot of free parameters u can use

same person scanned with three diff parameters

same algorithm set to work on mri data can give different answers based on which parameter used to acquire it (keep in mind)

29
Q

what is the MNI space?

A

need common coordinate frame -> how homologous anatomy is over time — need way to create this reference system

30
Q

how was the MNI space derived?

A

initially derived by aligning 300 brains and saying that this is the normative anatomy of the brain

can then look at mean morphology

31
Q

what is the common work flow? (5)

A
  1. principle is the same — you get volume from scanner and want to align it to a space
  2. normalize it across scans
  3. do some linearization/transformation
  4. use algorithm to classify the grey and white voxels
  5. smooth out and by voxel/voxel level, run stats (color map — high = lot of difference)
32
Q

how do you detect changes in cortical thickness?

A

surface representation is just points in space
- can go and measure differences btw white and black matter surface
- can then put this in a color map

algorithm creates mesh
- see points that define the surface (edges of triangles)
- ask algorithm to fold the sphere to match the voxel representation of the white matter
- constantly creating more points that allow it to fold more
- big brain morphologies are the ones done earlier on

33
Q

what was the conclusion of the study on brain morphology and individual history?

A

one fold increase in terms of brain volume in rats housed in the complex house

34
Q

explain the study on the V5 and juggling

A

made people learn to juggle

scan1-2 increase in grey matter (region V5 —> regions is like motor and visual)

sees rapid growth (3% change) in this part of the brain over time

then asks people to stop juggling and three months later → this part of the brain is still enlarged compared to baseline

35
Q

explain the study on musicianship and the brain

A

differences in brains of musicians (uni level) vs control

see increased cortical thickness in PFC and regions involved in working memory and involved in sound processing

representation is far more compact (not diffuse)

suggests that years of training have specific imprint on the brain that doesnt exist in non-musicians

36
Q

what has neuroimaging taught us about the brain’s development?

A

brain changes a lot in early life

things that change are grey matter, myelin, white matter concentration

brain is continuously refining across lifespan

white matter conc peaks in end middle age

37
Q

explain the study on adhd and cortical thickness

A

brain matures later in adhd kids

in PFC there’s almost a 3y delay of reaching cortical thickness as normal developing kids

38
Q

what are the grey matter deficits in childhood onset schizophrenia (COS)?

A
  1. parietal-frontal progression of GM loss during adolescence (from age 12-16)
  2. GM loss declines and is circumscribed to prefrontal and temporal cortices by age 24
39
Q

how is GM affected in siblings of COS patients?

A

healthy COS siblings show cortical GM deficits in early ages that NORMALIZE by age 18

40
Q

is ASD homogeneous or heterogenous?

A

heterogenous; many factors contribute

41
Q

what are the sex differences in ASD prevalence?

A

prevalence: 1 in 68

The ratio of males to females diagnosed is about 4:1 (more pronounced in higher functioning (6-9:1), but closer in lower functioning (2:1))

42
Q

what theory might explain the gender differences in ASD?

A

female protective effect hypothesis

43
Q

what is the female protective effect hypothesis? (4)

A

States that females may be protected against neurodevelopmental disorders

May take more autism risk factors (genetic or environmental) to manifest the autistic phenotype

Females have higher threshold for the amount of genetic liability or risk factors needed to cause autism (dotted line), so affected less often than males

Supported by the fact that, presumably due to this higher burden or number of risk factors, when females are affected, tend to be more severe

44
Q

how does cortical thickness and age affect asd? (3)

A

Other studies have examined the neuroanatomy of autism into development and adulthood and found significant effects, in particular cortical thickness

But inconsistent: many studies have found greater thickness in individuals with ASD, but others have found thinner cortex or no differences.

age seems to be more important: found greater CT but effects normalize with age

45
Q

how might IQ and cortical thickness relate to asd?

A

may have moderating effect: CT positively correlated with IQ in controls, but not in ASD (no or negative relations)

46
Q

what is the impact of motion on cortical morphometry?

A

Participant motion is:
Associated with reduced average cortical thickness

Higher in clinical populations

More strongly correlated with CT than volumetric estimates

47
Q

what is the quality control procedure for motion?

A

Assign motion score (4 point scale)

Two independent raters of motion
→ QC manual, trained raters, checked reliability after first 100 scans
→ Consensus score

Objective exclusion cut-off

looking for ringing and blurring

48
Q

what is the vertex-wise meta-analysis technique?

A

Random effects meta-analysis used to account for inter-site differences and heterogeneity of sample

Multiple linear regression across 80,000 vertices conducted within each site

Cohen’s d effect size calculated per site at each vertex and pooled in meta-analysis

False Discovery Rate (FDR) for multiple comparisons correction

49
Q

what is advantageous of the vertex-wise analysis? (2)

A

allows to treat sites as separate studies and analyse that way

to avoid confounds of scanner and variability of demographics between sites

50
Q

what is the diagnosis main effect in CT and adhd? (3)

A

First, we looked at the main effect of DX in all subjects, controlling for age and sex, and found widespread increases in CT across in the brain in ASD

These are maps of q-values across the brain, regions where significant diffs between ASD and controls - all increases in ASD

All coming slides are 5 or 10% FDR, and min 1%, all increases in ASD

51
Q

what sex differences in ASD did they find in the study (using vertex analysis)?

A

We then broke this down to look at males and females separately, and here is what we found in the males – shown at 10% FDR

Again, increases in CT, primarily in inferior frontal and superior temporal regions.

Finally as cubic, effects even stronger, still strongest at 8, decreasing at 12 and 16, still small areas of significance visible at 20 (drop after 40)

PSYT 500 (11 decks)

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