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