1. Simultaneous recording of EEG and BOLD responses
Why and How

2. Synopsis Motivation and perspectives Technical Setup
EEG data processing
The gradient artifact
Technical prerequisites: synchronization
Artifact removal and data quality
The ballistocardiographic artifact
Current studies
Conclusions

3. Motivation and perspectives
Achieving both high spatial and temporal resolution
Shed light on the foundations and interrelations of MEG, EEG and fMRI

4. Motivation and perspectives
Is there a (partial) correspondence of fMRI and EEG/MEG?
fMRI indirectly inferes neural activity via BOLD-reponse (neurovascular coupling)
EEG/MEG more directly reflect neural activity (apical EPSPs…)
large scale
synchrony
neural firing
rates

5. Motivation and perspectives
Basic applications
fMRI-informed source reconstruction
parametric designs and EEG-fMRI covariation
single-trial coupling of EEG and fMRI

6. Motivation and perspectives
Higher order models
compound neural mass and hemodynamic models
joint ICA
parallel ICA

7. Motivation and perspectives
Clinical relevance???
Original Motivation:
Mapping epileptic zones
Recent „clinical“ research:
Movement disorders (cortical myoclonus)
Brain-computer interfaces (Biofeedback)

8. Motivation and perspectives
Measurement techniques and applications
separate recordings of EEG and fMRI (two sessions)
interleaved recordings (EEG in “silent periods”)
simultaneous recordings (both modalities continuously measured)

9. Motivation and perspectives
Continuous/simultaneous measurements:
temporal correlation of EEG and fMRI
avoidance of order effects
semi-optimized design
strongly degraded signal quality (especially EEG)
contaminated EEG
contaminated EEG
raw „clean“ EEG
raw „clean“ EEG

10. Combined EEG – fMRI Recordings Actual Status Hard- and Software
Technical Setup
Combined EEG – fMRI Recordings Actual Status Hard- and Software

11. EEG-Recording Technical Setup
System Components (BrainAmp MR plus, Brain Products GmbH):
EEG amplifier unit, 32 channel, fMRI approved (GE, Bruker, Siemens and Phillips scanner), accumulator driven
EEG cap (EASY Cap), 32 channel (plus EOG, ECG), modified system, sintered Ag/AgCl sensors, 10 kOhm for EEG cables, 15 kOhm for EOG/ECG cables, 3 different sizes
Sync-Box (Frequency divider), synchronization between MR scanner and EEG data recording
EEG-Data acquisition computer + Recording Software
BrainAmp I/O USB Adapter, interface between all other components

12. Technical Setup
EEG cap

13. Technical Setup
EEG Amplifier

14. Stimulation Modes Technical Setup Visual Stimulation:
Stimulation Computer (Presentation) -> Beamer -> Ground Glass -> Mirror (800x600 pixel) -> Subject
Auditory Stimulation:
Stimulation Computer (Presentation) -> Audiometer -> Audio Amplifier -> MR compatible stereo Head Phones -> Subject
Tactile Stimulation:
Stimulation Computer (Presentation) -> pneumato-tactile Stimulator -> 8 (finger) membranes -> Subject
Components which are inside the MR measurement chamber are emphasized in green

15. Tactile Stimulation Technical Setup
driven by compressed air
up to eight independent output channels
integrated TTL trigger control unit

16. MRI compatible opto-electrical Response Unit
Technical Setup
MRI compatible opto-electrical Response Unit
2 response panels (shape is adapted for left and right hand)
Each panel provides 2 response buttons (best fitting for index and middle finger)
Response panels are connected to opto-electrical transducers via fiber optical cables (inside MR chamber)
Response signals are recorded by Stimulation and Recording Software in order being referable during later analysis

17. Technical Setup
Response Unit

18. Triggering / Synchronization
Technical Setup
Triggering / Synchronization
(Hardware) Trigger Generators:
Stimulation Computer: event coding and timing via Presentation port codes
Response Unit: response coding trigger
SyncBox: periodic sync trigger generated from scanner electronic pulse to synchronize the EEG signal sampling by the MR scanner rate (requisite for scanner artefact rejection)
fMRI-Scanner: volume trigger representing MR volume scan onset time (used for scanner artefact rejection and event timing in Presentation)
All triggers are represented in the recorded EEG data set and one can refer to them during the subsequent data analysis (artefact rejection, averaging etc.).

19. Technical Setup fMRI Scanner MR chamber Electronic Sync preAmp
Stimulation
Audio Amplifier
Opto-elect Transducer
Pneumato-tactile Stimulator
Response
Buttons
Clips
Membranes
Head Phones
Beamer
fMRI
Scanner
Electronic
EEG-Amplifier
Volume Trigger
Sync preAmp
I/O-USB Adapter
Sync Box
EEG Recording

20. Online Recording Setup
Technical Setup
Online Recording Setup

21. Combined EEG – fMRI Recordings Data quality
Technical Setup
Combined EEG – fMRI Recordings Data quality

22. EEG data correction Major artifacts “gradient artifact”
induced currents due to gradient switching
“ballistocardiographic artifact”
movement of conductive material in static magnetic field
vibrations due to active helium pump

23. EEG data correction The “gradient artifact” slice selection:
frequency of slice acquisition
e.g. TR = 2s, 28 slices – 14 Hz (and harmonics)
spatial encoding within a slice:
usually phase encoding
e.g. 64 × 64 Matrix – 64 × 15 = 960 Hz (not recorded)

24. EEG data correction The “gradient artifact”
technical artifact – rather invariant
correction via subtraction of channel-specific templates
problem 1: subject motion changes position of cables/electrodes
foam cushions
problem 2: differential timing of EEG sampling and fMRI acquisition
EEG/MR Synchronisation – “SyncBox”

25. EEG data correction
synchronized
unsynchronized

26. corrected EEG with sluggishly fixed electrode
EEG data correction
corrected EEG with sluggishly fixed electrode
contaminated EEG
raw „clean“ EEG
corrected EEG

27. EEG data correction

28. EEG data correction The ballistocardiographic artifact
movement of conductive material in static magnetic field
cardiac-related axial head motion
pulsatile movement of the scalp
electromagnetic induction due to blood flow

29. EEG data correction The ballistocardiographic artifact
correction via subtraction of channel-specific templates
Problems:
biological artifact – high degree of variability
template stability over time – motion induced changes

30. BCG artifact – after template subtraction
EEG data correction
BCG artifact – after template subtraction
BCG artifact

31. EEG data correction

32. EEG data correction The ballistocardiographic artifact
further improvements may be obtained via:
removal of residual BCGA via ICA
Optimal Basis Set (OBS – channelwise temp. PCA)
OBS - ICA

33. EEG data correction BCG artifact – after additional ICA filtering
BCG artifact – after template subtraction

34. EEG data correction BCG artifact – after additional ICA filtering
BCG artifact – after template subtraction

35. EEG data correction The ballistocardiographic artifact
further improvements may be obtained via:
removal of residual BCGA via ICA
Optimal Basis Set (OBS – channelwise temp. PCA)
OBS – ICA
“automatized” component identification
correlating the raw ECG-trace with time courses of independent component
correlating BCGA-topography with IC weighting matrix

36. EEG data correction

37. additional ICA filtering
EEG data analysis
subtraction only
additional ICA filtering

38. EEG data analysis

39. EEG data analysis
amplitude
time

40. EEG data analysis
standard fMRI
single trial fMRI

41. Conclusions Current studies:
Tactile Stop-Signal task (executive functions)
Affective conditioning
Language processing
Planned study:
Resting state/default mode network