basis of m/eeg signal david sutton lucy ferguson
TRANSCRIPT
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Basis of M/EEG Signal
David SuttonLucy Ferguson
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Overview
• Introduction• EEG vs. MEG• Background• Signal• EEG• MEG• Disadvantages• Advantages• Summary
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EEG
Neuroscience - nervous system
• neural communication
• pyramidal neurons
Physics - “knowledge of nature”
• electromagnetism
• technology
http://opencc.co.uk/blog/out-of-touch-manual-keypads-and-controllers-face-competition-from-new-hands-free-computer-interfaces/
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MEG
• Measures the magnetic fields generated by neuronal activity – generally the field generated by post-synaptic currents across pyramidal neurons (EEG measures the current itself)
• Measured outside the head
http://www.admin.ox.ac.uk/estates/capitalprojects/previouscapitalprojects/megscanner/
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EEG vs. MEG
Barnes, ???
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EEG - History
Anatomy & Physiology: invasive vs. non-invasive
1875 - Richard Caton first observes that an electrical current can be detected on skull and brain
1890 - Adolf Beck reports electrical activity in animals
1912 - Pravidich-Neminsky published first EEG study
1914 - Cybulski and Jelenska-Macieszyna record seizures
Role of EEG in neuroimaging: identify neural correlates
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MEG - History1962: Discovery of the Josephson effect
1968: David Cohen makes first MEG recordings of human α-rhythm
1970: Superconducting quantum interference device (SQUID) invented by James
Zimmerman
1972: SQUID technology is applied to MEG recording
1979: 3-channel SQUID system is built
1992: First whole-cortex MEG system (64 channels) is built
2000: First investigational foetal MEG system is used
http://www.fil.ion.ucl.ac.uk/spm/course/slides12-meeg/01_MEEG_Origin.ppt
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What Can EEG Measure?
• Measures electrical potential differences between pairs of scalp electrodes
• Gyri (radial)
• EPSP apical dendritic trees
• Depolarisation of dendrites
• Current volume conductor
• Extracellular currents = issue
Tiege & Zlobinski, 2006
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What Can EEG Measure? (Continued)
Tiege and Zlobinski, 2006
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Electrical Current Magnetic Field
http://www.youtube.com/watch?v=CPj4jJACeIs
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What Can MEG Measure?
The magnetic field generated by an electrical current exits the head, where it can be measured
N.B. MEG is less sensitive to radial sources
Easier to detect fields generated in sulci rather than in gyri
Unlike the EEG signal, the magnetic field measured by MEG is not distorted by the different conductive properties of the head and scalp
http://www.ctf.com/images/megbasics.jpg
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What Can MEG Measure? (Continued)
http://www.youtube.com/watch?v=CPj4jJACeIs
Monophasic signals
Post-synaptic potential
Cell alignment
http://www.cns.nyu.edu/~david/courses/perception/lecturenotes/brain/brain-slides/Slide12.jpg
Pyramidal cells
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Deeper Structures
(Hillebrand & Barnes, 2002) http://ilabs.washington.edu/what-magnetoencephalography-meg
MEG is less sensitive to magnetic fields generated by deeper sources
Sensitivity loss is proportional to squared distance between source &
sensor
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EEG - Instrumentation
• Cap (different numbers of electrodes)
• Gel
• Thin sticks
• Reference Montage
(specialneedsdigest.com) (biosemi.com)
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EEG - Instrumentation
(Continued)
10-20 System
Electrode placement occurs over frontal, parietal, temporal,
central, and occipital regions (see Friedrich &
Friederici, 2005)
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EEG - Machine
• 8 – 64 identical 8 – 64 identical channels recording channels recording simultaneously from simultaneously from as many different as many different pairs of electrodespairs of electrodes
• Electrodes & Electrodes & electrode boardelectrode board
• AmplifiersAmplifiers• FiltersFilters• Pen & chartdrive Pen & chartdrive
(screen)(screen)Tiege and Zlobinski, 2006
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EEG Frequency SpectrumWaveWave
ssFrequFrequ
encies encies per per secondsecond
AmplitAmplitude in µVude in µV
CharacteristicsCharacteristics
Beta-Beta-waveswaves
14 - 30 5 - 50, mostly
below 30
Sharp spike-waves over 35 Hz,
Frontocentral, precentral & posterior
Criteria of light sleep stages
Alpha-Alpha-waveswaves
8 - 13 5 - 120, mostly below 50
Posterior-dominant, awake, eyes closed, mental inactivity, physical relaxation
Theta-Theta-waveswaves
4 - 7 20 - 100 Strictly rhythmic or highly irregular
Awake & drowsiness or light sleep stages
Delta-Delta-waveswaves
0,5 - 3 5 - 250 Abnormality in waking adults,
Accompaniment of deep sleep
GammGamma-wavesa-waves
31 - 60 -10 Legality of appearance and site not well established
Tiege and Zlobinski, 2006
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EEG Frequency Spectrum
Tiege and Zlobinski, 2006
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EEG Studies
Muzur, Pace-Schott, and Hobson, (2002)Role of Prefrontal Cortex in Sleep
•Mediates normal sleep physiology, dreaming, and sleep-deprivation phenomena
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EEG Studies (Continued)
Janz, (2000)
Epilepsy with grand mal on awakening and sleep-waking cycle
•Strong association between sleep deprivation and seizures in idiopathic generalised epilepsy
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MEG - The Magnetic Field
The magnetic fields generated by neural activity are significantly smaller than those created by other objects in the environment
Susceptible to interference from electrical equipment, cars, participant’s heartbeat, etc.
Interference from heartbeat
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Noise Reduction: Magnetically Shielded Room (MSR)
http://web.mit.edu/newsoffice/2012/mcgovern-institute-honors-meg-inventor.html
5 layers with different magnetic properties to protect from different frequencies of magnetic interference
Spherical room = greater magnetic efficiency
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Measuring The Magnetic Field: SQUIDs
http://www.csiro.au/~/media/CSIROau/Images/Maps%20%20Graphs/SQUID_CESRE_ind/High_Resolution.gif
Superconducting Quantum Interference Device
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Flux Transformers
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Magnetometer
http://www.youtube.com/watch?v=CPj4jJACeIs
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Axial Gradiometer
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Planar Gradiometer
http://www.youtube.com/watch?v=CPj4jJACeIs
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CTF 275 Channel Omega System
http://www.youtube.com/watch?v=CPj4jJACeIs;
275 axial gradiometers
Reference sensors for noise cancellation
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http://www.scholarpedia.org/article/Magnetoencephalogram
https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&ved=0CCwQFjAA&url=http%3A%2F%2Fwww.fil.ion.ucl.ac.uk%2Fspm%2Fcourse%2Fslides12-meeg%2F01_MEEG_Origin.ppt&ei=NCn5UqjzH4uThgeRkoCYBA&usg=AFQjCNFnyD2zlZ71ivl6aYa82Ha_8txR3Q&bvm=bv.60983673,d.ZG4
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MEG Output
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Event-Related Potentials (ERP)
•Many trials over the same time
averaged together•Waves described after polarity and Waves described after polarity and
latency (e.g. N400), method of release latency (e.g. N400), method of release
(mismatch negativity) and (mismatch negativity) and
psychophysiological correlativespsychophysiological correlativesTiege and Zlobinski, 2006
Duncan et al., 2009
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Evoked vs. Induced Effects
http://imaging.mrc-cbu.cam.ac.uk/meg/IntroEEGMEG#megrecordings
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MEG - PTSD Study
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Disadvantages
• Forward Problem• Inverse Problem• Spatial Resolution• Artifacts• EEG
• Preparation• Current distortion
• MEG• Money• Deep sources
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Forward Problem
http://buybrainfuelplustoday.com/wp-content/uploads/2013/11/brain.jpg
?Determining output which will be generated by a particular primary current source
MEG is relatively straightforward compared to EEG
UNIQUENESS – there is only one possible solution
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Inverse Problem
?
?
?
?
?
Determining the source of the observed magnetic field
NONUNIQUENESS – there are an infinite number of solutions for this problem
An “ill-posed” problem
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Inverse Problem (Continued)
http://thedabbler.co.uk/wp-content/uploads/2011/10/cows.jpghttp://www.youtube.com/watch?v=vh5kZ4uIUC0
SMALL FAR AWAY
E.G. VISION
We can use a priori knowledge of object properties to determine whether something is small vs. far away…
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Overcoming Spatial Resolution
•Lewine et al., 2007• Traumatic brain injury• MRI, SPECT, and MEG
•Salek-Haddadi et al., 2006
http://www.google.co.uk/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&docid=IPagwvFKn_bviM&tbnid=qodUT1bbVAf9FM:&ved=0CAQQjB0&url=http%3A%2F%2Ffmri.uib.no%2Findex.php%3Foption%3Dcom_content%26view%3Darticle%26id%3D71%26Itemid%3D88&ei=mi76UsqlC8OU0AXmhYHQDg&bvm=bv.61190604,d.ZG4&psig=AFQjCNF5h277Ok7ERPQrbQEUCdpYjezXfQ&ust=1392213661800215
• EEG-correlated fMRI• Focal epilepsy
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Advantages
• Temporal resolution• Non-invasive• Quiet• EEG
• Cheap• Clinical implications
• MEG• Preparation• Head distortion
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Summary: EEG vs. MEG
Both EEG and MEG use the same underlying signal, but generate different outputs
http://www.theredmenmovie.com/2009/11/magnetoencephalography-meg-scanner.html
http://www.fastcompany.com/3008499/tech-forecast/these-brain-scanning-neuro-toys-are-about-change-everything#4
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Thank You Gareth!
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Resources
http://youtu.be/eq8wHT8qYJsMEG brain waves
http://youtu.be/vniog26Qp94
Preparing for an EEG
http://youtu.be/bO-_ZtIxcr0
EEG Demonstration Video
http://youtu.be/YqO-Z7kDeoA
MEG and epilepsy
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Sourcesde Tiege, X., & Zlobinski, I. (2006). What do we measure with EEG and MEG?. Unpublished manuscript, Institute of Neurology, University College London, London, United Kingdom. Retrieved from http://www.google.co.uk/url?sa=t&rct=j&q=eeg tiege&source=web&cd=8&ved=0CGYQFjAH&url=http://www.fil.ion.ucl.ac.uk/~mgray/Presentations/What%20are%20we%20measuring%20with%20EEG%20and%20MEG.ppt&ei=pYv6UqOVLJ DB7AaLzoHIBA&usg= AFQjCNGmvbxOQZX o09xqh50mL3BLNLytDQ&bvm=bv.61190604,d.ZGU.
Friedrich, M., & Friederici, A. D. (2005). Phonotactic knowledge and lexical-semantic processing in one-year-olds: Brain responses to words and nonsense words in picture contexts. Journal of Cognitive Neuroscience, 17(11),
1785-1802. doi: 10.1162/089892905774589172.
Duncan, C. C., Barry, R. J., Connolly, J. F., Fischer, C., Michie, P. T., Näätänen, R., ... & Van Petten, C. (2009).
Event-related potentials in clinical research: guidelines for eliciting, recording, and quantifying mismatch negativity, P300, and N400. Clinical Neurophysiology, 120(11), 1883-1908.
Janz, D. (2000). Epilepsy with grand mal on awakening and sleep-waking cycle. Clinical Neurophysiology, 111, S103-S110. doi: 10.1016/S1388-2457(00)00409-0
Kolb, B., & Whishaw, I.Q. (2009). Fundamentals of human neuropsychology (6 th ed.). New York, NY: Worth Publishers
Lewine, J. D., Davis, J. T., Bigler, E. D., Thoma, R., Hill, D., Funke, M., ... & Orrison, W. W. (2007). Objective documentation of traumatic brain injury subsequent to mild head trauma: multimodal brain imaging with
MEG, SPECT, and MRI. The Journal of head trauma rehabilitation, 22(3), 141-155. doi: 10.1097/01.HTR. 0000271115.29954.27
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Muzur, A., Pace-Schott, E. F., & Hobson, J. A. (2002). The prefrontal cortex in sleep. Trends in cognitive sciences, 6(11), 475-481. doi: 10.1016/S1364-6613(02)01992-7.
Purves, D., Brannon, E.M., Cabeza, R., Huettel, S.A., LaBar, K.S., Platt, M., & Woldorff, M.G. (2008). Principles of cognitive
neuroscience. Sunderland, MA: Sinauer Associates, Inc.
Singh, K.D. (2006). Magnetoencephalography. In Senior, C., Russell, T., & Gazzaniga, M.S. (Eds.), Methods in Mind,
(291-325). Cambridge, MA: The MIT Press.
Sources (Continued)
Vrba, J. (2002). Magnetoencephalography: The art of finding a needle in a haystack. Physica C: Superconductivity, 368(1-4), 1-9
Salek-Haddadi, A., Diehl, B., Hamandi, K., Merschhemke, M., Liston, A., Friston, K., ... & Lemieux, L. (2006). Hemodynamic correlates of epileptiform discharges: an EEG-fMRI study of 63 patients with focal epilepsy. Brain research, 1088(1), 148-166.)
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Sources (Continued)
http://www.fil.ion.ucl.ac.uk/spm/course/slides12-meeg/01_MEEG_Origin.ppt
http://www.ctf.com/images/megbasics.jpg
http://www.cns.nyu.edu/~david/courses/perception/lecturenotes/brain/brain-slides/Slide12.jpg
specialneedsdigest.com
biosemi.com
http://www.bem.fi/book/14/14.htm
http://ilabs.washington.edu/what-magnetoencephalography-meg
http://www.fastcompany.com/3008499/tech-forecast/these-brain-scanning-neuro-toys-are-about-change-everything#4
http://www.theredmenmovie.com/2009/11/magnetoencephalography-meg-scanner.html
http://www.scholarpedia.org/article/MEG
http://rmp.aps.org.libproxy.ucl.ac.uk/pdf/RMP/v65/i2/p413_1
http://www.youtube.com/watch?v=CPj4jJACeIs
https://www.ucl.ac.uk/stream/media/swatch?v=8af2e6e28e4d
http://www.martinos.org/meg/pdfs/2003EncycNeuroSc.pdf
http://imaging.mrc-cbu.cam.ac.uk/meg/IntroEEGMEG#megrecordings
http://www.ctf.com/company.html
http://opencc.co.uk/blog/out-of-touch-manual-keypads-and-controllers-face-competition-from-new-hands-free-computer-interfaces/
http://www.admin.ox.ac.uk/estates/capitalprojects/previouscapitalprojects/megscanner/