NIH's 275-channel MEG system

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NIH's 275-channel MEG system
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MEG Lab Features

• Stim computer (Ika) boots Win98 or WinXP, tasks
  are written using Presentation software (can also
  use Matlab, Linux, etc.).
• Visual stimuli via projection screen, driven by
  Ika. Auditory stimuli via pneumatic headphones,
  driven by Ika or arbitrary phono/RCA jack input.
• Secondary computer interface (e.g., laptop)
  including sound and light.
• Other stimulators Grass electrical stimulator,
  air-puff stimulator.
• Response devices optical button boxes (one
  handheld), dual motion sensors, eye tracker,
  pneumatic pads, x-y joystick.
• Optical sensor auditory trigger for precise
  timing.
• All devices interface both with Ika and the MEG
  system.

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CTF 151 Channel array
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Synthetic Aperture Magnetometry
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Spatial resolution increases with the number of
MEG channels
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N-Back Working Memory Task Details

• Sixteen 22 sec blocks of alternating 0-back and
  2-back
• Stim one of four numbers (0.5 duration, 1.8 sec
  ITI)
• normal volunteers strongly right handed
• 2-back accuracy greater than 65

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Methods N-Back Task
1.8 s
1.8 s
1.8 s
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Stimulus
1.8 s
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2
3
1
1.8 s
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4
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2
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Response
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2
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0-BACK
1 none
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4 1
1-BACK
2 4
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4 2
3 4
Time
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DataEditor window with marks in the stimulus and
ADC channels
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Data Analysis

• SAM Synthetic Aperture Magnetometry
• Optimum spatial filter for each .75 cm voxel
  calculated from dual state freq domain covariance
  matrix
• Time windowsblock(14 sec), stim (500 msec), resp
  (500 msec)
• Theta, alpha, beta, gamma, freq bands
• Group 3d map from Talairach aligned volumes using
  AFNI, n18 NC
• Bluedesynch Redpower increase

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Group Analysis

• MRIs Talairach aligned in AFNI
• SAM image z-score normalized by pooled variance
• AFNI 3dmean averaged warped SAM volumes
• Normalized t statistic (3dttest) to threshold
  group mean map

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fMRI Processing

• 3T GE EPI-RT, 24 slices, TE 30, TR 2000, FOV 24
  cm, voxel 3.75x3.75x6 mm, 64 x 64 matrix
• Structurally aligned, smoothed and normalized to
  MNI space, SPM99
• Single subj block design contrast for 2back gt
  0back
• Group second level analysis at approx pgt.001

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• MEG and fMRI
• 2-back vs 0-back memory task, Block design
• same 12 subjects, group map at p approx lt.001

SAM 500 msec window on response, Beta
desynchronization
SPM T map 2bgt0b SPM99 t 4.0 Z 3.10, p
0.001, k gt 10
CBDB and NIMH MEG Core
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Time-Frequency Analysis of Auditory Click Trains

• Broadband clicks, 1 ms duration
• Binaurally presented
• Trains of 5 clicks with 250 ms ISI

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Beamformer Virtual Channels for an Auditory
Metronome
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Advanced Signal Processing FieldTrip
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