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PS3035 > Neuroimaging > Flashcards

Neuroimaging Flashcards

1
Q

What 3 methods can be used for brain lesion studies?

A
  • Physical
  • Pharmalogical
  • Reversible (cooling or transcranial magnetic stimulation )
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2
Q

What are the advantages of brain lesion studies?

A
  • Can provide information on function

- Carry out otherwise unethical studies

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3
Q

What are the disadvantages of brain lesion studies?

A
  • Difficult to say how precise/specific they are

- Is the effect due to solitary contribution or an imbalance effect

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4
Q

What is transcranial magnetic stimulation?

A
  • The induction of an electric current in nearby neurons using a rapidly changing magnetic field
  • Can activate (e.g muscle reponses) or inhibit b
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5
Q

What are the advantages of TMS?

A
  • Ability to study healthy patients with a controlled stimulation
  • Inexpensive
  • Excellent temporal resolution
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6
Q

What are the disadvantages of TMS?

A
  • Low spatial resolution
  • Possible risk of inducing epilepsy, effects on mood, local headaches
  • Long term effects are not well established
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7
Q

What is transcranial direct current stimulation (tDCS)?

A

Using + and - patches to induce an electron flow in the brain which can be
Cathodal - hyperpolarisation of neuronal membranes decreasing firing rate
Anodal - depolarisation of neuronal membranes increasing the firing rate

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8
Q

What are the advantages of tDCS?

A
  • Inexpensive

- Allow for controlled neuromodulation

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9
Q

What are the disadvantages of tDCS?

A
  • Low spatial resolution

- Cannot be used on patients with epilespy, implants or who are on medications

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10
Q

What are the two categories of neuroimaging techniques?

A
  • Hemodynamic

- Electromagnetic

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11
Q

How does PET work?

A
  • Ingestion of radioactively labelled material, emit positrons which are picked up
  • Active brain accumulates oxygen and glucose
  • Provides functional view with 45-60s integration period
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12
Q

What are the advantages of PET?

A
  • Allow measurement of metabolism and blood flow

- Can use in conjunction with behaviour and pharmalogical studies

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13
Q

What are the disadvantages of PET?

A
  • Expensive
  • Invasive (eposure to radiation)
  • Moderate spatial and poor temporal resolution
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14
Q

How does fMRI work?

A
  • Uses huge magnet to induce nuclear magnetic resonance phenomenon where protons align in parallel or anti-parallel in response to strong magnetic field
  • When RT is switched off measure time longitutional magnetization (T1) and transversal relaxation (T2) retun to normal
  • High concentration of H has high sensitivity to NMR therefore there are differences between oxy-haemoglobin and deoxy-haemoglobin
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15
Q

What are the possible issues with fMRI?

A
  • Indirect measure
  • Inhibitory activity may increase or decrease energy consumption
  • Susceptible to noise
  • Arbitrary thresholds for significance
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16
Q

What are the two methods in fMRI?

A

Subtraction method - experimental minus control activated areas
Region of interest - look at patterns of activation across different experimental conditions

17
Q

What is diffusion tensor imaging (DTI)?

A
  • Used to determine anatomical connections

- Uses stats to examine interrelationships between brain areas

18
Q

What are the advantages of fMRI?

A
  • Safe and therefore repeatable
  • High spatial resolution
  • Moderate temporal resolution
19
Q

What are the disadvantages of fMRI?

A
  • Expensive (uses He)
  • Movements are restricted
  • Claustrophobia
  • Large ammounts of acoustic noise (can’t carry out auditory experiments)
  • Fields can generate body heat
20
Q

What is spatial/temporal summation?

A

When action potentials summate either
temporally - close activity
spatial - summation of neurons in similar area firing at the same time

21
Q

What is EEG?

A

Measure summation of post-synaptic potentials

22
Q

What are the limitations of EEG?

A
  • Must be measuring an open field which is synchronously active and arranged perpendicular and close to the skull
  • Polarity sometimes not interpretable
23
Q

How are EEGs recorded?

A
  • Using reference electrode of minimal activity and measuring the difference
  • Standardised system “International 10-20 system” with 4 reference points: inion (back), nasion (eyes), and left and right perpendicular points
24
Q

What is the difference between EEG and ERP?

A

EEG - large voltage from large area of the brain

ERP - averaging across similar events timelocked to onset of the stimuli

25
Q

What are the assumptions of ERP?

A
  • That background varies randomly and is not time local

- Repetition of the same event will ellicit the same behavioural/brain response

26
Q

What is the potential issue with the assumptions of ERP?

A

Neuronal signals change when stimuli are presented repeatedly due to adaptation effects

27
Q

What are the components of an ERP?

A
  1. Anticipation response
  2. Early brain stem response
  3. Midlatency components related to the perceptual response
  4. Late commponents (+100ms) which are tak-related potentials
28
Q

How are ERPs labelled?

A
  • Polarity
  • Latency
  • Topography (spatial distribution across scalp)
29
Q

What are the advantages of EEG?

A
  • High temporal resolution

- Cheap and non-invasive

30
Q

What are the disadvantages of EEG?

A
  • Poor spatial resolution
  • Poor conductivity of certain tissues can cause distortion
  • ‘Inverse problem’ where we know how activity is distributed but are unclear on the source
  • Absence of difference does not necessarily mean there is no effect: could mean method is not sensitive enough
31
Q

How have ERPs called into question ‘free will’?

A
  • Libet experiment

- Readyness potential starts -550ms before consciously reported intention to act

32
Q

What is Magnetic-encephalography (MEG)?

A
  • Recording of electric/magnetic activity elicited by neurons
  • Measures mostly tangentially orientated neurons (parallel to the skull)
  • Very sensitive sensor (only small magnetic field)
33
Q

What are the benefits of MEG?

A
  • High temporal resolution
  • Easier to use than EEG
  • Magnetic fields aren’t as distorted as other brain tissues
34
Q

What are the disadvantages of MEG?

A
  • Expensive
  • Susceptible to magnetic artifacts
  • Participant head movements are highly restricted
35
Q

How does optical imaging work?

A
  • Use lazer diodes to shine light through tissue
    Can interact by:
    Scattering - neural tissue becomes more transparent when activated
    Absorption - in light spectra is related to bloos oxygenation
36
Q

What are the advantages and disadvantages of optical imaging?

A 
Advantages:
- Inexpensive and safe 
- Excellent spatial and temporal resolution 
Disadvantages 
- Limited penetration of tissue 
- Low transparency of white matter 
- Low signal to noise ratio

PS3035 (4 decks)

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