1 / 19

M/EEG Data: What are we measuring? Jason Taylor MRC Cognition and Brain Sciences Unit (CBU) Cambridge Centre for Agei

M/EEG Data: What are we measuring? Jason Taylor MRC Cognition and Brain Sciences Unit (CBU) Cambridge Centre for Ageing and Neuroscience (CamCAN) 19 January 2011 | SPM M/EEG Course | Brussels [ Much stolen from James Kilner, Jérémie Mattout, Olaf Hauk ]. M/EEG: What are we measuring?.

shanton
Télécharger la présentation

M/EEG Data: What are we measuring? Jason Taylor MRC Cognition and Brain Sciences Unit (CBU) Cambridge Centre for Agei

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. M/EEG Data: What are we measuring? Jason Taylor MRC Cognition and Brain Sciences Unit (CBU) Cambridge Centre for Ageing and Neuroscience (CamCAN) 19 January 2011 | SPM M/EEG Course | Brussels [ Much stolen from James Kilner, Jérémie Mattout, Olaf Hauk ]

  2. M/EEG: What are we measuring? • What do we want to measure? • How do we measure it? • What do we really measure? • What do we not measure? • Why don’t we use a different measure?

  3. What do we want to measure? - + = Electric dipole, with magnetic field produced according to the right-hand rule Current flow in apical denrites of cortical pyramidal cells (not action potentials)

  4. What do we want to measure? ~1 million synapses must be simultaneously active to be detected - + Along with the primary current, volume currents are induced in the surrounding tissues Luckily, there are ~10 million cells per mm2 with 1000s of synapses each.

  5. How do we measure it? 1771: Luigi Galvani (<- Bologna, Italy) experiments with ‘animal electricity’. 1840s, ’50s: Du Bois-Raymond (Berlin) and Helmholtz (Berlin) describe and quantify action potential. 1875: Richard Caton (Liverpool, UK ->) measures currents between the cortical surface and the skull (ECoG) in dogs, monkeys 1924: Hans Berger (<- Jena, Germany) records first EEG in humans, describes alpha and beta waves

  6. MCG: Cohen, Science (1967) (first: Baule & McFee in 1963, Syracuse, NY) MEG: Cohen, Science (1968) -- early days of MEG (and MCG) 1960s: David Cohen (<- MIT) MCG and MEG, pre-squid

  7. MCG: Cohen, Science (1967) (first: Baule & McFee in 1963, Syracuse, NY) MEG: Cohen, Science (1968) 1979: Joy Division (Manchester, UK) release ‘Unknown Pleasures’, featuring recordings of a pulsar on the album cover (obviously inspired by Cohen’s MEG waveforms ;-).

  8. -- and now, the SQUID! 1970: James Zimmerman (Ford Co., USA) invents the Superconducting Quantum Interference Device (SQUID), an ultrasensitive detector of magnetic flux Superconductivity is zero-resistance electrical conduction that (typically) occurs at extremely cold temperatures, near absolute zero. 1973: Brian Josephson (Cambridge, UK) awarded the Nobel prize for prediction (in 1962) of ‘tunnel effect’ between two superconducting materials separated by a thin insulating layer (‘Josephson Junction’) Brian Josephson

  9. -- and now, the SQUID! This -> is not it David Cohen knew something about extreme cold temperatures, having grown up in Winnipeg, Canada (incidentally also my home town), where it’s often -30°C for weeks at a time in the winter. Cohen (Science, 1972) describes the first SQUID-based 1-sensor MEG recording David Cohen http://www.etsy.com ‘squid hat’

  10. -- and now, the SQUID! MCG MEG

  11. MEG sensor types http://meg.aalip.jp/scilab/CoilType.html

  12. Elekta Neuromag Vector View System Sensor Array 102 magnetometers 204 planar gradiometers EEG Cap (70-channel montage shown)

  13. What do we really measure?

  14. -- methods for removing/avoiding noise Independent Component Analysis (ICA) Magnetically shielded room (MSR) VEOG Signal Space Separation (SSS) - Neuromag IC1 MEG1 Plus: Filtering, averaging, robust averaging,… Before /After IC1 removed MEG2 MEG3 MEG4

  15. What do we not measure? -- dipole orientation MEG vs. EEG - MEG is insensitive to (purely) radially oriented dipoles

  16. -- source depth MEG vs. EEG - MEG is insensitive to (purely) radially oriented dipoles - MEG is less sensitive to deep sources From Olaf Hauk: http://http://www.mrc-cbu.cam.ac.uk/research/eeg/eeg_intro.html

  17. -- cancelling sources MEG vs. EEG - MEG is insensitive to radially oriented dipoles - MEG is less sensitive to deep sources - NEITHER can detect closed (cancelling) sources Ahlfors et al., HBM 2010

  18. Why don’t we use a different measure?

  19. Thanks! - The End -

More Related