|
Table of Contents
|
Basic Information and Technical Material
The human brain is an extremely complex biological system performing sensory, motor, linguistic and cognitive functions with very rapid neural processes. For centuries, scientists, medical doctors, and philosophers have shown great interest in studying the relationship between the neurophysiological events in the brain and mental events that constitute our cognitive abilities and subjective experiences, producing many exciting discoveries as well as theories and speculations (Gazzaniga, 2004). However, understanding the spatiotemporal dynamics of brain activities remains one of the most intriguing challenges in modern science – how the brain accomplishes its tasks, how its abilities develop and decline, what underlies the various sensory, motor, cognitive and communicative impairments and deficits, and what methods can be selectively applied for the prevention and treatment of the disorders.
Anatomically, the complexity of brain activities involves a network of billions of highly specialized neurons that communicate with each other via trillions of synaptic connections. The inner workings of the neural network largely depend on chemically mediated electric processes, which can be measured online using invasive or noninvasive techniques at various levels. Magnetoencephalography (MEG) is a completely noninvasive imaging technique that measures the exquisitely small magnetic fields outside the brain produced by neuronal currents in many brain regions (Hämäläinen, Hari, Ilmoniemi, Knuutila, & Lounasmaa, 1993; Williamson, Hoke, Stroink, & Kotani, 1989). A closely related and complementary method, electroencephalography (EEG), measures the electric fields of the regional neural activities by using electrodes directly pasted on the scalp to assess brain function at a system level.
Both EEG and MEG are great research tools for cognitive brain studies where temporal information of the evoked brain activities is considered critical. This is due to the fact that both techniques can reveal the time course of neural activation with sub-millisecond accuracy. The recordings can be performed in the absence of any behavioral responses, which makes EEG and MEG suitable for studying populations across the life span in both research and clinical settings. Relatively speaking, the MEG signals are less affected by the individual anatomical differences such as tissue conductivity. When combined with magnetic resonance imaging (MRI) and functional MRI, MEG also has the advantage of providing highly reliable localization of neuronal activity within a few millimeters on an individual basis (Barkley, 2004; Baumgartner, 2004). However, the high cost and technicality associated with MEG equipment using conventional superconducting sensors has been a major limitation on its wide acceptance in practice.
Click here for publications from Zhang Lab using brain imaging methods
Electroencephalography (EEG) and Event-related Potential (ERP)
EEG Recording in Zhang Lab
| Equipment | |
|---|---|
  |
 |
| Asa-lab is suitable for experiments on both normal and clinical populations across the life span. Types of measurements range from Auditory Evoked Potentials, Visual Evoked Potentials, and complex paradigms on language and cognition. | Xsensor 3D Electrode Digitizer system; 7 WaveGuard caps for adults, children and infants |
| Stimulus presentation software | Analysis and graphics software |
| eevoke | Waveform analysis: ASA, BESA |
| Neurobehavioral system's Presentation | Time-frequency, ICA analysis: ASA, BESA, EEGlab |
| Matlab | Source analysis: ASA, BESA+Brain Voyager, MNE2.6 |
| Visual C++ | Customized analysis: Matlab, Systat, Microsoft Excel |
| E-prime 2.0 Professional | Graphics: Photoshop, Illustrator, CorelDraw, Matlab |
Magnetoencephalography (MEG) and functional Magnetic Resonance Imaging (fMRI)
| MEG at collaborating sites in Twin Cities, MN, Tokyo, Japan, and Helsinki, Finland |
|---|
    |
| 3T MRI at U of Minnesota; 1.5T MRI at Tokyo Denki University |
  |
| Analysis and graphics software |
| BESA+BrainVoyager, MNE2.6+freesurfer; Neuromag Software; Customized analysis in Matlab |
Anatomical MRI analysis methods
| Freesurfer |
|---|
  |
| lh.inflated | lh.pial | lh.white_matter | lh.sphere |
|---|---|---|---|
 |
 |
 |
 |
Freesurfer Procedures
- surface reconstruction
- inter-subject spherical averaging
- cortical thickness measurement
- volumetric analysis
- white matter
- cortical parcellation: cortical surface shape and folding analysis
- surface-based analysis
- subcortical segmentation
- diffusion analysis
- FS-FAST
Multimodal imaging
Multimodal imaging analysis in Zhang Lab requires knowledge of UNIX and Matlab. The software is installed on Mac Os10.5 macPro workstation with 16 Gb Ram.
MNE2.6 + Freesurfer + FSL (Software package only runs on UNIX/LINUX and Mac OS X systems)
MNE2.6 provides advanced MEG/EEG L2 minimum source estimates, which can be visually plotted in three formats:
- current amplitude in Minimum Norm Estimate (MNE)
- dynamical Statistical Parametric Mapping (dSPM)
-
- dSPM is a spatio-temporal map of converted Z scores relative to pre-stimulus baseline noise.
- dSPM is useful for fMRI & MEG integration or depth weighting with MEG alone to improve localization accuracy.
-
- standardized Low-Resolution Electromagnetic Tomography (sLORETA, a Bayesian method)
Sample dSPM result in the right hemisphere for vowel perception at 80.4 ms in one adult subject.
Toolboxes
These toolboxes require knowledge and programming skills in Matlab. Users who are not familiar with Matlab should use the user-friendly commercial software (ASA, BESA, and BrainVoyager). Zhang Lab has full licenses for the ASA, BESA and BrainVoyager software packages.
- EEGlab: An interactive Matlab toolbox for processing continuous and event-related EEG, MEG and other electrophysiological data incorporating independent component analysis (ICA), time/frequency analysis, artifact rejection, event-related statistics, and several useful modes of visualization of the averaged and single-trial data.
- Fieldtrip: Matlab toolbox for the analysis of MEG and EEG data, such as time-frequency analysis, source reconstruction using dipoles, distributed sources and beamformers and non-parametric statistical testing.
- Brainstorm: An integrated free Matlab toolkit dedicated to Magnetoencephalography (MEG) and Electroencephalography (EEG) data visualization and processing.
- SPM: A popular toolbox designed for the analysis of fMRI, PET, SPECT, EEG and MEG.
- Biosig: A toolbox for biomedical signal processing, featuring the analysis of biosignals such as the electroencephalogram (EEG), electrocorticogram (ECoG), electrocardiogram (ECG), electrooculogram (EOG), electromyogram (EMG), respiration, etc.
- Psychtoolbox: Visual stimulus generation and experimental design.
Online video of magnetoencephalography with Dr. Wenbo Zhang (MEG Director) and Dr. Robert Doss
Introduction to MEG, including a pediatric MEG imaging session at the Magnetic Source Imaging Lab at United Hospital in St. Paul.
Recommended Resources
The Talairach Daemon
This software is very useful for querying and retrieving data about brain structures transformed to the standard Talairach space. Please click here for download.
MEG Reviews
M. Hämäläinen, R. Hari, R. Ilmoniemi, J. Knuutila, and O. V. Lounasmaa, "Magnetoencephalography - theory, instrumentation, and applications to noninvasive studies of the working human brain," Reviews of Modern Physics, vol. 65, pp. 413-497, 1993.
S. Baillet, J. C. Mosher, and R. M. Leahy, "Electromagnetic Brain Mapping," IEEE Signal Processing Magazine, vol. 18, pp. 14 - 30, 2001.
M. Hämäläinen and R. Hari, "Magnetoencephalographic Characterization of Dynamic Brain Activation: Basic Principles and Methods of Data Collection and Source Analysis," in Brain mapping : the methods, A. W. Toga and J. C. Mazziotta, Eds. Amsterdam ; Boston: Academic Press, 2002.
Free MRI and fMRI online resources
Human Brain Function - Methods behind SPM by J. Ashburner, K. Friston, W. Penny et al.
MRI Physics - Professor Joseph Hornak's pages on advanced MRI physics
Introduction to MRI Physics - Animated
Matlab for CLA students (free of charge)
Please click here for instructions on how to download Matlab to your personal computer.
EEG/ERP and fMRI Books
Reference books and papers are available on the bookshelf in Room 46. Please do not take them away from the lab.
