Magnetoencephalography, Really Fast Fourier Transforms, and the Hunt for HFOs

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Magnetoencephalography,Really Fast Fourier
Transforms,and the Hunt for HFOs

• William F. Eddy
• Department of Statistics
• Machine Learning
• Biological Sciences
• Carnegie Mellon University
• Pittsburgh, PA
• bill_at_cmu.edu

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Special Thanks

• Anto Bagic, MD, Director CABMSI,UPMC
• Anna Haridis, MBA,MEG Coordinator,UPMC
• Jianming Wang, Ph.D., Tianjin University, PRC
• Bronwyn Woods, Graduate Student, CMU Neural
  Computation
• Shuhei Okamura, Graduate Student,CMU Statistics
• Erika Taylor, Graduate Student, CMU Psychology

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Outline

• Magnetoencephalography
• Fourier Transforms
• High Frequency Oscillations
• Success/Failure

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http//www.4dneuroimaging.com
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MEG

• MEG is most powerful technique for studying brain
  function non-invasively
• MEG records magnetic fields induced by
  synchronized neuronal activity seen outside of
  the skull
• MEG can attain a temporal resolution of a few
  milliseconds.
• MEG can monitor the activation of a neuronal
  population with a spatial resolution of several
  millimeters

(Cohen, 1972 Hamalainen et al., 1993 George et
al., 1995 Vrba Robinson, 2001 Pataraia et
al.,2002).
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Gradiometer Magnetometer
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Magnetically Shielded Room
(Cohen et al., 2002)
Image Courtesy of Elekta
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Magnetic Field Measurements

• Frequency
• 10 mHz (as low as 1 mHz for sleep spindles) to 1
  kHz.
• Field magnitudes
• 10 fT (10-15 T) for spinal cord signals to about
  a
• picotesla (10-12 T) for brain rhythms.
• The Earth 0.5 mT, the urban magnetic noise 1
  nT 1 ?T.
• The Environment/Brain Ratio 1 million 1
  billion.

(Nakaya Mori, 1992 Vrba Robinson, 2001)