The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Estimating Neural Currents from Neuromagnetic Measurements

Kimmo Uutela

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission for public examination and debate in Auditorium F1 at Helsinki University of Technology, Espoo, Finland, on the 18th of December, 2001, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-5699-1)   [573 KB]
Dissertation is also available in print (ISBN 951-22-5770-X)

Abstract

This thesis concerns three new methods for estimating the electrical activity of the human brain from the magnetic fields measured outside the head. The first method models the electrical activity as a combination of focal current dipoles and applies global optimization to estimate their locations without need for an initial solution. The second method is the minimum current estimate that is capable of modeling both focal and distributed electrical activity. The third method measures the movements of the head during the measurements and uses this information for more accurate estimates of the neural currents. The usability of the methods is demonstrated using simulations and measurements. The minimum current estimate is also applied to four experiments of cognitive processes in the human brain: one studying visuomotor interaction, second studying visual attention, third studying integration of auditory and visual representations of letters, and fourth studying observation of sign language in signing and non-signing subjects.

This thesis consists of an overview and of the following 7 publications:

  1. Uutela, K., Hämäläinen, M., and Salmelin, R. (1998). Global optimization in the localization of neuromagnetic sources. IEEE Trans. Biomed. Eng., 45:716-723.
  2. Uutela, K., Hämäläinen, M., and Somersalo, E. (1999). Visualization of magnetoencephalographic data using minimum current estimates. NeuroImage, 10:173-180.
  3. Uutela, K., Taulu, S., and Hämäläinen, M. (2001). Detecting and correcting for head movements in neuromagnetic measurements. NeuroImage, 14:1424-1431.
  4. Nishitani, N., Uutela, K., Shibasaki, H., and Hari, R. (1999). Cortical visuomotor integration during eye pursuit and eye-finger pursuit. J. Neurosci., 19:2647-2657.
  5. Vanni, S. and Uutela, K. (2000). Foveal attention modulates responses to peripheral stimuli. J. Neurophys., 83:2443-2452.
  6. Raij, T., Uutela, K., and Hari, R. (2000). Audiovisual integration of letters in the human brain. Neuron, 28:617-625.
  7. Levänen, S., Uutela, K., Salenius, S., and Hari, R. (2001). Cortical representation of sign language: Comparison of deaf signers and hearing nonsigners. Cerebral Cortex, 11:506-512.

Keywords: magnetoencephalography, inverse problem, minimum-norm estimate, multidipole model, head movements, visuomotor interaction, visual attention, audiovisual integration, sign language

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© 2001 Helsinki University of Technology

Last update 2011-05-26