meg data analysis with synthetic aperture magnetometry (sam) dr. tom holroyd nimh meg core facility
TRANSCRIPT
MEG Data Analysis with MEG Data Analysis with Synthetic Aperture Synthetic Aperture
Magnetometry (SAM)Magnetometry (SAM)
Dr. Tom HolroydDr. Tom Holroyd
NIMH MEG Core FacilityNIMH MEG Core Facility
NIH's 275-channel MEG system
MEG Lab FeaturesMEG Lab Features Stim computer (Ika) boots Win98 or WinXP, tasks are written Stim computer (Ika) boots Win98 or WinXP, tasks are written
using Presentation software (can also use Matlab, Linux, etc.).using Presentation software (can also use Matlab, Linux, etc.).
Visual stimuli via projection screen, driven by Ika. Auditory Visual stimuli via projection screen, driven by Ika. Auditory
stimuli via pneumatic headphones, driven by Ika or arbitrary stimuli via pneumatic headphones, driven by Ika or arbitrary
phono/RCA jack input.phono/RCA jack input.
Secondary computer interface (e.g., laptop) including sound and Secondary computer interface (e.g., laptop) including sound and
light.light.
Other stimulators: Grass electrical stimulator, air-puff Other stimulators: Grass electrical stimulator, air-puff
stimulator.stimulator.
Response devices: optical button boxes (one handheld), dual Response devices: optical button boxes (one handheld), dual
motion sensors, eye tracker, pneumatic pads, x-y joystick.motion sensors, eye tracker, pneumatic pads, x-y joystick.
Optical sensor & auditory trigger for precise timing.Optical sensor & auditory trigger for precise timing.
All devices interface both with Ika and the MEG system.All devices interface both with Ika and the MEG system.
CTF 151 Channel array
Flux transformers used to transport flux to the SQUID loop.
(a) shows a simple one coil flux transformer, (b) a first order gradiometer.
Synthetic Aperture Magnetometry
Spatial resolution increases with the number of MEG channels
N-Back Working Memory N-Back Working Memory Task DetailsTask Details
Sixteen 22 sec blocks of Sixteen 22 sec blocks of alternating 0-back and 2-backalternating 0-back and 2-back
Stim: one of four numbers (0.5 Stim: one of four numbers (0.5 duration, 1.8 sec ITI)duration, 1.8 sec ITI)
normal volunteers strongly right normal volunteers strongly right handedhanded
2-back accuracy greater than 65%2-back accuracy greater than 65%
Methods: N-Back Task
12 3
4
1.8 s
12 3
4
1.8 s
3 12 3
4
1.8 s
12 3
4
1.8 s
12
4
1.8 s
3
Stimulus
Response
0-BACK
1-BACK
1
none4
12
44
2 3
4
Time
DataEditor window with marks in the stimulus and ADC channels
Data AnalysisData Analysis SAM: Synthetic Aperture SAM: Synthetic Aperture
MagnetometryMagnetometry Optimum spatial filter for each .75 Optimum spatial filter for each .75
cm voxel calculated from dual cm voxel calculated from dual state freq domain covariance state freq domain covariance matrixmatrix
Time windows:block(14 sec), stim Time windows:block(14 sec), stim (500 msec), resp (500 msec)(500 msec), resp (500 msec)
Theta, alpha, beta, gamma, freq Theta, alpha, beta, gamma, freq bandsbands
Group 3d map from Talairach Group 3d map from Talairach aligned volumes using AFNI, n=18 aligned volumes using AFNI, n=18 NCNC
Blue=desynch; Red=power Blue=desynch; Red=power increaseincrease
Group AnalysisGroup Analysis
MRI’s Talairach aligned in AFNIMRI’s Talairach aligned in AFNI SAM image z-score normalized by SAM image z-score normalized by
pooled variancepooled variance AFNI 3dmean averaged warped AFNI 3dmean averaged warped
SAM volumesSAM volumes Normalized t statistic (3dttest) to Normalized t statistic (3dttest) to
threshold group mean mapthreshold group mean map
fMRI ProcessingfMRI Processing
3T GE EPI-RT, 24 slices, TE 30, TR 3T GE EPI-RT, 24 slices, TE 30, TR 2000, FOV 24 cm, voxel 2000, FOV 24 cm, voxel 3.75x3.75x6 mm, 64 x 64 matrix3.75x3.75x6 mm, 64 x 64 matrix
Structurally aligned, smoothed and Structurally aligned, smoothed and normalized to MNI space, SPM99normalized to MNI space, SPM99
Single subj block design contrast Single subj block design contrast for 2back > 0backfor 2back > 0back
Group second level analysis at Group second level analysis at approx p>.001approx p>.001
SPM T map 2b>0b {SPM99 t ~ 4.0; Z≡ ~ 3.10, p ~0.001, k > 10}
CBDB and NIMH MEG Core
MEG and fMRIMEG and fMRI2-back vs 0-back memory task, Block design2-back vs 0-back memory task, Block design
same 12 subjects, group map at p approx same 12 subjects, group map at p approx <.001<.001
SAM 500 msec window on response, Beta desynchronization
Broadband clicks, 1 ms durationBroadband clicks, 1 ms durationBinaurally presentedBinaurally presentedTrains of 5 clicks with 250 ms ISITrains of 5 clicks with 250 ms ISI
Time-Frequency Analysis of Time-Frequency Analysis of Auditory Click TrainsAuditory Click Trains
Low frequency component High frequency component
5 Clicks – 250ms ISI 4-6 seconds between click trains
Stimuli
Beamformer Virtual Channels for an Auditory Metronome
Gamma Sources
Time-Frequency plots using the Stockwell Transform
Advanced Signal Processing: FieldTripAdvanced Signal Processing: FieldTrip
NIMH MEG Core NIMH MEG Core
FacilityFacility
Dr. Richard Coppola, Dr. Richard Coppola,
DirectorDirector
Dr. Tom Holroyd, Staff Dr. Tom Holroyd, Staff
ScientistScientist
Dr. Fred Carver, System Dr. Fred Carver, System
AnalystAnalyst
Judy Mitchell-Francis, Lab Judy Mitchell-Francis, Lab
MgrMgr
Cate Reynolds, Post-Bac Cate Reynolds, Post-Bac
IRTAIRTA
CBDB Neuroimaging J.H. Callicott B.A. Verchinsky S. Sust
CBDB Sib Study M. Egan D.R.
Weinberger