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18 Cards in this Set
- Front
- Back
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What is MEG? |
Magnetoencephalography - measures neural activity by measuring the changing magnetic field produced by brain - precise time measurement (ms) |
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EEG measures... |
Electrical currents (AP) |
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MEG measures.. (2 readouts) |
MAGNETIC FIEEELDS |
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Both EEG and MEG are... |
non-invasive, detecting post-synaptic currents of pyramidal cells (cortex) |
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How are magnetic fields detected? |
by SQUIDs - Superconducting Quantum Interference Device (scanner has 300 SQUIDs) |
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How are background magnetic fields suppressed? |
Shielding - metal room Gradient measures - isolate rapid fields Electronically - software to remove 50hz main lines |
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2 ways of using MEG |
Temporal analysis (evoked recordings) Spatial analysis (dipole modeling) |
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Evoked recordings |
present stimulus record multiple times average the result |
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In MEG, there are two types of detectors for evoked recordings.. |
- two readouts: Gradiometers (200 channels/recordings) Magnetometers (100 channels/recordings) |
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Sometimes waveforms are presented topographically (from top of head) |
*Similar waveforms appear in similar regions/sources |
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Dipole modelling |
MRI scans image of brain Computer analyses MEG recording - locates separate sources |
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Limitation of Dipole modeling - Ill-posed problem |
- different dipole arrangements can give rise to the same magnetic fields = ill-posed inverse problem (working backwards) |
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Limitation (2) of Dipole modeling |
neural activity not always localised to a single cortical area |
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MEG can only detect dipoles that are... |
aligned radially (sulci) |
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EEG= Gyri MEG= Sulci Neither MEG/ EEG can detect .... |
neural activity deep within brain |
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Localising neural activity MEG has slightly better ____ resolution than EEG, but fMRI is much better at showing which parts of the brain is being activated |
Spatial |
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Both EEG and MEG have good ____ resolution |
Temporal |
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Halgren used MEG to find how long it took for the Fusiform Face Area to process a face... how long? |
165 ms |
