Transcript MEG/EEG Group - University of Pittsburgh

MEG/EEG Module
Trainees
Kai Hwang
Tina Rasmussen
Thanks to:
TA
Instructor
Gus Sudre
Bronwyn Woods
Bill Eddy, Ph.D.
Anna Haridis
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, preprocessing 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.
•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
Fast: ISI = 100ms,
Duration = 300ms.
Nothing due to time constraint.
Simultaneous MEG/EEG measurement
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
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
Average of 191 trials
Right Middle
Average of 119 trials
Can MEG localize 4 quadrants
of visual space?
Upper left
Upper right
Bottom 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
Electrode O2 (EEG059) is placed
over the right occipital lobe.
5 consecutive stimuli:
• First stimulus always at bottom left
• Position of next 4 varies randomly
• ISI = 100ms, Duration= 300ms.
What have we learned?
• Experiments:
Data recording setup
Simultaneous MEG/EEG experiments
• Signal processing/analysis:
Signal cleaning (SSS, continuous HPI, filtering)
Event-related potentials
Source estimation/localization
Time-frequency analysis
• Analysis tools:
MNE (GUI, batch scripts)
Shell scripting (bash and C shell)
Matlab toolbox (FieldTrip)
Toe tapping
Somatosensory Stimulation
Right 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.