MEG/EEG ModuleTrainees

Kai Hwang

Tina Rasmussen

TA

Gus Sudre

Bronwyn Woods

Instructor

Bill Eddy, Ph.D.

Anna Haridis

Thanks to:

Goals• Learn the basics of EEG/MEG

– Why? Excellent temporal resolution, direct and noninvasive measurement of neuronal activity

– How? Used simple motor, somatosensory, visual paradigms to learn data collection, pre-processing and analysis

• Easy to run, predictable results

Tasks: motor, visual, somatosensory

Task Parameters We’ll present…

Paced finger tapping:Index finger, middle finger, big toe.

A visual cue to indicate tap right or left finger.ISI = 800ms

Source localization result of right index, right middle finger tapping.

Visual checkerboard:Checkerboard stimuli shifted randomly between 4 quadrants of visual fields.

Slow: ISI = 1sec,Duration = 300ms.

Fast: ISI = 100ms,Duration = 300ms.

•Source localization of 4 quadrants of

visual field.•The effect of averaging and artifact rejection on sensor waveform.•Time frequency analysis in sensor space

Electrical stimulation:Index finger, middle finger, big toe.

ISI = 492 ms, Duration = 10 ms

Nothing due to time constraint.

Simultaneous MEG/EEG measurement

Experiences:• EEG head cap was very stiff. It did not fit well to

the head for some subjects.• MEG head position indicator (HPI) coils could

not be well localized by the MEG scanner, when they were glued to the EEG head cap

Solution to both problems:• Glue the EEG electrodes and the HPI coils

directly onto the subject’s scalp

Simultaneous MEG/EEG measurement

Processing Steps

• Preprocessing– Spatial filtering (SSS)– Temporal filtering (0 – 40Hz)

• Off-line averaging– By trial type (different finger, visual quadrant)– Reject trials with artifacts (EOG, ECG, etc)

• Source localization– MNE, dSPM

• Time-frequency analysis– Fieldtrip (Matlab)

Can MEG distinguish motor regions of different fingers?

Right Index Right Middle

Average of 191 trials Average of 119 trials

Can MEG localize 4 quadrants of visual space?

Upper right

Bottom left

Upper left

Bottom right

Average of 240 trials

120ms after stim. onset

How many events are needed to obtain a stable average waveform?

Top right quadrant

Artifact rejection for EEG signals

Temporal variation of EEG activity over the visual cortex

5 consecutive stimuli:

• First stimulus always at bottom left

• Position of next 4 varies randomly

• ISI = 100ms, Duration= 300ms.

Electrode O2 (EEG059) is placed

over the right occipital lobe.

What have we learned?• Experiments:

Data recording setupSimultaneous MEG/EEG experiments

• Signal processing/analysis:Signal cleaning (SSS, continuous HPI, filtering) Event-related potentialsSource estimation/localizationTime-frequency analysis

• Analysis tools: MNE (GUI, batch scripts)Shell scripting (bash and C shell) Matlab toolbox (FieldTrip)

Toe tapping

Somatosensory StimulationRight ToeRight Toe

Somatosensory Stimulation

Right Middle

Right Middle

SSS or no SSS?

Right index tapping. White = no SSS, yellow= SSS on average, blue SSS before averaging

MEG1821

cHPI (motion correction)

• Noisy!

Time-frequency analysis: EEG signals

Fast:

Temporal variation of EEG activity over the visual cortex

• 3 consecutive stimuli

• First stimulus always at top right

• Next 2 shifted randomly

• ISI = 100ms, Duration= 300ms.