Event related synthetic aperture magnetometry samerf
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Event-related Synthetic Aperture Magnetometry (SAMerf). Outline. Review of traditional SAM Introduction to SAMerf Cheyne et al. motor experiment Sliding window SAMerf. Review of traditional SAM. Estimates equivalent current dipole source power within specified frequency bands

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Outline
Outline

  • Review of traditional SAM

  • Introduction to SAMerf

  • Cheyne et al. motor experiment

  • Sliding window SAMerf


Review of traditional sam
Review of traditional SAM

  • Estimates equivalent current dipole source power within specified frequency bands

  • Based on sensor covariance in time windows

  • Uses optimal spatial filters to estimate source power on a grid of voxels



How do we increase temporal resolution
How do we increase temporal resolution?

  • Sliding window SAM

    • Calculate SAM images for small overlapping time windows

  • Virtual channels

    • Use the SAM spatial filters to estimate time series



How can we increase signal to noise in a virtual channel
How can we increase signal-to-noise in a virtual channel?

  • Average - either in the temporal or frequency domain

  • Averaging in time will produce an evoked response (and ignore induced activity)


Introduction to samerf
Introduction to SAMerf

  • Traditional SAM is performed on time windows and frequency bands of interest

  • Virtual channels are created for each voxel

  • The virtual channels are averaged to generate an event-related response (ERF)

  • Amplitudes of the ERFs at small time windows are used to produce 3D maps


Cheyne et al motor experiment
Cheyne et al. motor experiment

Spatiotemporal mapping of cortical activity accompanying voluntary movements using an event-related beamforming approach

Douglas Cheyne, Leyla Bakhtazad, William Gaetz

Neuromagnetic Imaging Laboratory, Hospital for Sick Children Research Institute, Toronto, Ontario, Canada

Hum Brain Mapp. 2006 Mar;27(3):213-29.






Sliding window samerf
Sliding window SAMerf

  • Activity is averaged over a small time window

  • The averaging window is slid to observe temporal changes

  • Good for increasing signal-to-noise and characterizing high frequency bursts


5 Clicks – 250ms ISI

4-6 seconds between click trains

Low frequency components

Low frequency components

Stimuli

Five Click Auditory Experiment

High frequency component

Low frequency component




Right IFG Gamma-band: 25-50Hz


Summary
Summary Gamma-band: 25-50Hz

  • Use traditional SAM to find power changes in frequency bands

  • Use SAMerf to localize evoked fields and phase-locked activity


Thanks! Gamma-band: 25-50Hz


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