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methods of cognitive neuroscience > Task 4 > Flashcards

Task 4 Flashcards

1
Q

What is an MEG?

A
  • used to detect tiny magnetic fields generated from the weak electric impulses, transmitted between brain cells
  • related to ERP
  • the electrical current associated with synaptic activity produces small magenetic fields that are perpendicular to the current (measures via SQUIDs)
  • MEG traces can be recorded and averaged over a series of trials, to obtain event-related fields
  • use a neuromagnetometer
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2
Q

What are SQUIDs?

A
  • Superconducting Quantum Interference Devices
  • pick up magnet fields generated by electrical currents in the brain
  • the magnetic fields are transmitted to the SQUID by means of a superconducting flux transformer
  • samples offer a range of locations: the distribution of electrical currents inside the brain are able to be accurately calculated
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3
Q

What is Femto Tesla ?

A
  • unit for magnetic fields
  • 1/10th billion the strength of earth´s magnetic field
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4
Q

What is are the measurements of EEG and MEG?

A

EEG:
- direct measure of activation
- electrical current stemming from synaptic activity
- precisely coincides with neural activity
- from sulci and gyiri

MEG:
- direct measure of activation
- magentic fields perpendicular to direction of electric current
- precisely coincides wuth neural activity
- only from suli

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4
Q

What is the difference between MEG vs. EEG ?

A
  • MEG is better in locating, where the particular activity is occuring (= less distortion) -> MEG and brain tissues are transparent to the magnetic field (! not the case for EEG)
  • MEG only measures the tangential currents (even when noise occurs)
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4
Q

What is more sensitive EEG or MEG ?

A
  • EEG is able to more reliable pick up deeper sources in the brain (that might be radially oriented)
  • MEG only displays surface parallel neurons
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4
Q

What are frequencies?

A
  • low frequency oscilliations
    > from larger neuronal populations
    > show large, synchromised amplitudes
    > thea, delta
  • high frequency oscilliations
    > from smaller neuronal assemblies
    > show smaller amplitues due to higher desychnronisation in underlying neuronal activity
    > beta, gamma
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4
Q

What are the similarities between EEG and MEG?

A
  • both have a high temporal resolution
  • both have a limited spatial resolution
  • both require the person to sit upright
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4
Q

What is the relationship between oscillations and MEG? What is the relationship between oscillations and EEG?

A
  • ## in adults the amplitude of normative EEG oscillations lies between 10 and 100 uV
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4
Q

What are frequency bands?

A
  • delta band (1-4Hz)
  • Theta Band (4-8Hz)
  • Alpha Band (8-13Hz)
  • Beta Band (13-30Hz)
  • Gamma Band (36-44Hz)
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4
Q

What are pros and cons about MEG?

A

+ same temporal resolution as ERP, but more reliable in detecting the source
+ non-invasive

  • flow must be parallel to the surface of the scull
  • to be effective, a magnetically shielded room is required
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4
Q

What happens during sleep?

A
  • Delata Bands
  • theta bands
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4
Q

What happens during activation?

A
  • beta band replaces alpha bands
  • gamma bands = associated with brain activation
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4
Q

What is the difference between frequency - amplitude - phase?

A
  • frequency and amplitude are analysed through spectral analysis
  • frequency (wie oft)
  • amplitude (wie stark)
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4
Q

What are applications of MEG?

A
  • attitudes
  • affective priming
  • social categorisation
  • stereotyping
  • cortex muscle coherence
  • action-viewing and mirror neurons
  • clinical applications (epiolepsy, tumors)
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4
Q

How are MEG and attitudes related?

A
  • P3 can assess attitudes -> N170
  • sensitivity to contextual inconsistency
  • used to measure implicit attitudes
  • oddball paradigm
4
Q

what is the relevance of power?

A

Alpha power asymmetry index
- investigates frontal symmetry
- derive from subtracting the natural log of the lest hemisphere power value from the natural log of the right hemisphere power value
- lnR - lnL
- positive value = greater right activity
- negative value = greater left activity

4
Q

How are MEG and social categorisation related?

A

a study investigated the affective congruency effect (investigates social cognition + priming)

-> post priming causes fast categorisation, which can be explained through the proximity of congruent primes and targets in a semantic network

4
Q

What is a time-frequency analysis?

A
  • developed because spectral analysis provides information about the frequency composition of EEG ossciliations but cannot give information , when frequency shifts occur
  • STFT (short time Fourier transform): for computation of a Fast Fourier transform (FFT) based time-dependent spectrum = spectrogram
  • Wavelet analysis: allows a more adaptive time-frequency approach affording flexible resolution -> EEG signals are seen as shifted and scaled mathematical functions
4
Q

How are MEG and stereotyping related?

A
  • intergroup attitudes and goals influence facial perceptions
  • early perceptual bases may be contributing to downstream racial prejduice and stereotyping
4
Q

what are Delta bands?

A
  • 1-4Hz
  • low frequency, high amplitude inhibitory rhythm
  • sleep, proximity of brain lesions
4
Q

How are MEG and affective priming related?

A
  • Affective congruency effect:
    > an affective target word is categroised in terms of valence
    > more quickly, when preceded by prime words of the same valence (congruent trials)
  • categorisation is facilitated due to the proximity of congruent primes and targets in a semantic network
  • suggests the locus for the effect in the evaluative categoriation process
  • LRP
  • N2
4
Q

What are Theta Bands?

A
  • 8-8 Hz
  • low frequency, high amplitude
  • mostly sleep, but 2 types during wakefulness
4
Q

What are Alpha Bands?

A
  • 8-13Hz
  • relaxed wakefulness, cognitive inactivity
  • greatest amplitude over posterior regions
  • different apha subbands (low - suppression/ upper - desynchronisation)
5
Q

What are Beta Bands?

A
  • 13-30Hz
  • high frequency, small amplitude
  • symmetric fronto-central distribution
  • replaces alpha rhythm due to cognitive activity
  • increased excitattory activity coming with focused attention, diffuse arousal
6
Q

What are Gamma Bands?

A
  • 36-44Hz
  • high frequency, small amplitude
  • attention, arousal, object recognition
  • directly associated with brain activation
  • reflect large scale integration + synchrony among widely distributed neurons
7
Q

What are spectral analysis

A
  • based on the notion that any oscillatory activity can be characterisde by the sum of different sinusoidal waves with distinct frequencies and amplituedes
  • = A method to provide inofmration about the frequency composition of EEG oscillations
  • FFA (= fast fourier transform): coefficients indicate the strength of the siganl at a given frequency, in order to estimate the contribution of different frequencies

methods of cognitive neuroscience (9 decks)

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