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Techniques in Neuroscience > The living brain > Flashcards

The living brain Flashcards

1
Q

Who were the early anatomists and their respective views of the brain?

A

> Aristoteles (384-322 BCE): brain = secondary organ

> Galen (2nd century): brain = siege of the mind

> Da Vinci (14th-17th century): early form of structural brain imaging
- revived interest in anatomy studies

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2
Q

What were lesion studies (e.g. Phineas Gage)?

A

Study of functional deficits after brain damage

-> understand brain-behaviour relationship

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3
Q

What was the main drawback of lesion studies?

A

Information for precise location of lesion only available after patient’s death

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4
Q

Who was the pioneer of functional brain imaging?

A

Angelo Mosso (19th century)

  • italian physiologist
  • linked blood flow to cognition
  • linked brain pulsations to brain activity: in fontanels of newborns and exposed brain of patients with deficits
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5
Q

What was Angelo Mosso’s 1882 machine?

What was his idea with this machine?

A

Weighing brain activity with the balance
- idea: increased blood flow to the brain linked to cognitive functions will tilt the balance

-> similarity to modern MRI scanner

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6
Q

Who realised the first medical X-ray?

A

Wilhelm Röntgen (German physicist)

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7
Q

What was the main drawback in X-rays used for medical diagnostics?

A

Lack of X-ray contrast within the skull

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8
Q

Who invented the X-ray derived techniques - answering the lack of X-ray contrast within the skull?

A

Walter Dandy (American neurosurgeon - 1919):

  • Ventriculography
  • Pneumoencephalography
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9
Q

What were the techniques of ventriculography and pneumoencephalography invented by Walter Dandy (1919)?

A

> Ventriculography:
generating contrast to remove ventricular cerebral spinal fluid (CSF) through a hole in the skull

> Pneumoencephalography:
same but for lumbar puncture

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10
Q

What were the issues with Walter Dandy’s ventriculography and pneumoencephalography (1919)?

A

> Risky procedures: triggered significant side effects (e.g. death)… still in use until 1970s

-> replaced by modern modalities (e.g. CT scanning)

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11
Q

What made measuring brain functioning in real time possible in the 20th century - invented by who?

A

Electroencephalography

  • Hans Berger: German psychiatrist and physiologist
  • First human EEG published in 1924
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12
Q

What are two early milestones of EEG history?

A

> First measure of epileptic spikes (1934)

> Characterisation of the several stages of sleep (1953)

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13
Q

What is the main use of EEG in a clinical setting?

A

Detect and characterise epileptic seizures

- combined with fMRI: used to identify the whole network of brain regions involved

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14
Q

Who developed the first commercial CT scanner (1967)?

A

Godfrey Hounsfield

- English electrical engineer

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15
Q

What does CT stand for? How is it also called?

A

Computed tomography

  • X-ray CT
  • computerised axial tomography (CAT)
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16
Q

When was developed the world’s first whole-body CT scanner?

A

1973

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17
Q

How does a CT work?

A

Combine X-rays from many directions to reconstruct the volume of interest in slices

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18
Q

What is a PET scan?

A

1970s: Positron Emission Tomography

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19
Q

How does a PET scan work?

A

PET = nuclear medicine technique

  • tagging an active molecule with short-lived radioactive tracer
  • injecting the tracer in the body
  • Tissue tracer concentration and location computed by detecting the GAMMA rays emitted as byproduct of the decay of the radioactive tracer
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20
Q

What is the disadvantage of PET?

A

Radioactive tracers decay quickly -> need to be produced onsite in a cyclotron
=> PET is the most expensive neuroimaging technique

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21
Q

What is mostly used in today’s neuroimaging research?

A

Magnetic Resonance Imaging (MRI)

22
Q

What are the different ways MRI is used to study brain structure?

A

> High resolution anatomical scanning

> Looking at microstructure changes in diffusion tensor imaging (DTI)

> Mapping white matter tracks in the brain

23
Q

What is fMRI and what does it measure?

A

Functional MRI:

  • measures dynamic changes every couple of seconds in the whole brain
  • during experimental tasks (task-based fMRI)
  • or at rest (resting state fMRI)
24
Q

What causes the difference in neuro-image quality?

A

Variation in spatial and temporal resolution

25
Q

What are the characteristics of structural imaging in spatial and temporal resolution?

A

> Low temporal resolution: takes minutes to acquire

> High spatial resolution: great amount of details to acquire

26
Q

What are the characteristics of functional imaging in spatial and temporal resolution?

A

> High temporal resolution: takes seconds to acquire

> Low spatial resolution: poor amount of details

27
Q

What is multimodal imaging?

What does it allow researchers to do?

A

Acquiring several structural scans and some fMRI tasks
- or combined EEG and fMRI

-> researchers can look at their problems from different angles

28
Q

What are the 4 characteristics of EEG?

A
  1. Non-invasive
  2. Records brain activity
  3. Signal is picked up by multiple electrodes in different locations
  4. Sensors covered with gel to make them have good contact
29
Q

What are the advantages of EEG?

A
  • Cheap
  • Somewhat portable
  • Measures brain activity at the millisecond scale

=> Highest temporal resolution

30
Q

What are the disadvantages of EEG?

A

Signal is measured only on the surface of the scalp leading to lack of localisation of brain function, especially in the deep brain

-> does not provide accurate localisation of brain function
=> Lowest spatial resolution

31
Q

What are the levels of spatial and temporal resolution and tolerance needed for EEG?

A

> Lowest spatial resolution
Highest temporal resolution
Low tolerance needed

32
Q

What is MEG and what are its 3 characteristics?

A

Magnetoencephalography (MEG)

  1. close to EEG, but measures changes in magnetic field
  2. subjects position their head in MEG helmet
  3. Liquid helium used to cool down sensitive magnetic sensors
33
Q

What are the levels of spatial and temporal resolution, and tolerance needed for MEG?

A

> Lowest spatial resolution
Highest temporal resolution
Medium tolerance needed (higher than EEG)

34
Q

What are the 4 characteristics of PET?

A
  1. Invasive
  2. Use of radiopharmaceuticals to measure physiological processes
  3. Possible to compute tissue tracer concentration
  4. Radioactive tracers decay quickly -> need to be produced onsite in cyclotron

-> PET is the most expensive neuroimaging technique

35
Q

What are some of the most commonly used tracer used in PET to characterise the distribution of dopamine in the brain

A
  • 18F-DG: Fluorine-18 fluorodeoxyglucose

- 18F-DOPA

36
Q

What are the levels of spatial and temporal resolution, and tolerance needed for PET?

A

> High spatial resolution (brain measure on millimetre scale)
Lowest temporal resolution (only able to measure brain function in 10/20 seconds)
High tolerance needed (invasive method with injection of radioactive tracers)

37
Q

What is fNIRS and what are its 4 characteristics?

A

Functional near infrared spectroscopy (fNIRS)

  1. Non-invasive optical imaging technique
  2. Detects changes in brain activity through neuromuscular coupling with near-infrared light
  3. Based on BOLD effect
  4. Particularly suited for infant brain (small and thin skull)
38
Q

What are the limitations of fNIRS?

A
  • Near-infrared light does not penetrate deep through the skull or brain
  • Limited spatial resolution (few sensors)
39
Q

What are the levels of spatial and temporal resolution, and tolerance needed for fNIRS?

A

> Low spatial resolution
High temporal resolution
Low tolerance needed

40
Q

What are the 4 characteristics of fMRI?

A
  1. Based on BOLD effect
  2. Based on oxy- and deoxyhaemoglobin magnetic properties
  3. Indirectly measures brain activity from regional changes in magnetism
  4. Used for psychiatric and neurological disorders, and to study healthy brain processes
41
Q

What are the levels of spatial and temporal resolution, and tolerance needed for fMRI?

A

> Highest spatial resolution
Low temporal resolution
Medium tolerance needed

42
Q

What is the order of methods from highest to lowest spatial resolution?

A

fMRI > PET > NIRS > EEG - MEG

43
Q

What is the order of methods from highest to lowest temporal resolution?

A

EEG - MEG > NIRS > fMRI > PET

44
Q

What is the order of methods from lowest to highest cost?

A

EEG (£20 000) < fNIRS < MEG < fMRI < PET (million £)

45
Q

What is the power of the magnetic field of an fMRI, and how is it generated?

A

> 1.5 to 3 Tesla: 30 000 times stronger than Earth’s magnetic field (equivalent to the ones in junkyards)

> Generated by superconductive magnet always ‘on’, that requires cooling by liquid helium

-> Patients have to be MR-compatible

46
Q

What kind of technique is fMRI?

A

A contrast technique

- based on the principle of cognitive subtraction

47
Q

What is the principle of cognitive subtraction?

A

Different experimental conditions associated to different cognitive states are statistically contrasted to find out which parts of the brain respond to what is different between the conditions

48
Q

What are the magnetic properties of oxy- and deoxyhaemoglobin?

A

> oxyHb (O2Hb): diamagnetic = not magnetic

> deoxyHb (HHb): paramagnetic = magnetic

49
Q

What is the BOLD effect, and how is it associated to fMRI?

A

Blood Oxygenation Level Dependent

  1. deoxyHb perturbs the local magnetic field
  2. brightness in an fMRI image is linked to the level of local magnetic perturbation
  3. The more magnetic perturbation, the darker the image
50
Q

How does fMRI measuring work?

A

Local increase in brain activity triggers:
1. Initial use of the local pool of O2 (in first 100 milliseconds)
- more deoxyHb than at rest -> more magnetic perturbation than at rest -> image darker than at rest
= initial dip in BOLD effect

  1. Larger increase in regional O2 delivery than what is needed (to overcompensate the use of local O2 during brain activity)
    - local area flooded by oxyHb -> less regional deoxyHb than at rest -> less magnetic perturbation than at rest -> image brighter than at rest during brain activity

-> we measure these slower processes

51
Q

What is the fMRI processing stream?

A
  1. Raw data
  2. Preprocessing: to increase signal to noise ratio
    - > remove the effect of head movement, cardiac pulsations, respirations, etc.
  3. Single subject level analysis:
    - subjects’ brain activity in relation to the given experimental model -> general linear model (GLM)
  4. Group level analysis
52
Q

What do most fMRI papers include?

A
  1. Brain maps
  2. Result tables
  3. Illustrative plots

Techniques in Neuroscience (6 decks)

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