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Simultaneous recording of EEG and BOLD responses Why and How.

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Presentation on theme: "Simultaneous recording of EEG and BOLD responses Why and How."— Presentation transcript:

1 Simultaneous recording of EEG and BOLD responses Why and How

2 1. Motivation and perspectives 2. Technical Setup 3.EEG data processing i. The gradient artifact Technical prerequisites: synchronization Artifact removal and data quality ii. The ballistocardiographic artifact 4. Current studies 5. Conclusions Synopsis

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

4 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 Motivation and perspectives

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

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

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

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

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

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

11 EEG-Recording System Components (BrainAmp MR plus, Brain Products GmbH): 1.EEG amplifier unit, 32 channel, fMRI approved (GE, Bruker, Siemens and Phillips scanner), accumulator driven 2.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 3.Sync-Box (Frequency divider), synchronization between MR scanner and EEG data recording 4.EEG-Data acquisition computer + Recording Software 5.BrainAmp I/O USB Adapter, interface between all other components Technical Setup

12 EEG cap

13 Technical Setup EEG Amplifier

14 Stimulation Modes 1.Visual Stimulation: Stimulation Computer (Presentation) -> Beamer -> Ground Glass -> Mirror (800x600 pixel) -> Subject 2.Auditory Stimulation: Stimulation Computer (Presentation) -> Audiometer -> Audio Amplifier -> MR compatible stereo Head Phones -> Subject 3.Tactile Stimulation: Stimulation Computer (Presentation) -> pneumato-tactile Stimulator -> 8 (finger) membranes -> Subject Technical Setup Components which are inside the MR measurement chamber are emphasized in green

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

16 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 Technical Setup

17 Response Unit

18 Triggering / Synchronization (Hardware) Trigger Generators: 1.Stimulation Computer: event coding and timing via Presentation port codes 2.Response Unit: response coding trigger 3.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) 4.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.). Technical Setup

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

20 Technical Setup Online Recording Setup

21 Combined EEG – fMRI Recordings Data quality Technical Setup

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 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) EEG data correction

24 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 EEG data correction

25 synchronized unsynchronized EEG data correction

26 contaminated EEGraw clean EEGcorrected EEG corrected EEG with sluggishly fixed electrode EEG data correction

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

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

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

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

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

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

35 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 EEG data correction

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37 subtraction only additional ICA filtering EEG data analysis

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39 time amplitude

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


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