# Presentation: 146443

**MEG Data Analysis with Synthetic Aperture Magnetometry (SAM)**
- Dr. Tom Holroyd
- NIMH MEG Core Facility

## 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.

## CTF 151 Channel array

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## Synthetic Aperture Magnetometry

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## Spatial resolution increases with the number of MEG channels

## 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%

## 			Methods: N-Back Task			

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_**Stimulus**_

_**Response**_

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- Time

## DataEditor window with marks in the stimulus and ADC channels

## Data Analysis

- SAM: Synthetic Aperture Magnetometry
- Optimum spatial filter for each .75 cm voxel calculated from dual state freq domain covariance matrix
- Time windows:block(14 sec), stim (500 msec), resp (500 msec)
- Theta, alpha, beta, gamma, freq bands
- Group 3d map from Talairach aligned volumes using AFNI, n=18 NC
- Blue=desynch;  Red=power increase

## Group Analysis

- MRI’s 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 > 0back
- Group second level analysis at approx p>.001

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

- CBDB and NIMH MEG Core

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

-  SAM  500 msec window on response, Beta desynchronization

## Time-Frequency Analysis of Auditory Click Trains

- Binaurally presented
- Trains of 5 clicks with 250 ms ISI

## Low frequency component

- High frequency component

## Beamformer Virtual Channels for an Auditory Metronome

## Gamma  Sources

- Time-Frequency plots using the Stockwell Transform

## Advanced Signal Processing: FieldTrip

## NIMH MEG Core Facility

- Dr. Richard Coppola,  Director
- Dr. Tom Holroyd, Staff Scientist
- Dr. Fred Carver, System Analyst
- Judy Mitchell-Francis, Lab Mgr
- Cate Reynolds, Post-Bac IRTA