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Dynamic Imaging of Brain Function with MEG and EEG

Speaker: Matti S. Hamalainen, Ph.D. Abstract:
Timing is essential for proper brain functioning. Magneto-encephalo- graphy (MEG) and electroencephalo-graphy (EEG) are at present the only noninvasive human brain imaging tools that provide submillisecond temporal accuracy and thus help to unravel dynamics of cortical function. MEG and EEG reflect the electrical currents in neurons directly, rather than the associated hemodynamic or metabolic effects. Unfortunately, the underlying current distribution cannot be recovered uniquely, even if the magnetic field (MEG) and the electric potential (EEG) were precisely known everywhere outside the head. Therefore, appropriate constraints must be applied to facilitate the solution. The current distribution can be modeled either by a constellation of discrete focal sources or by a continuous distribution. In both approaches an accurate forward field computation model is required to predict signals generated by a given source cur-rent distribution. The computational complexity of the MEG and EEG source estimation problem is due to two basic factors. First, the data to be modeled consist of 300-400 channels sampled at a rate of 200-2000 Hz acquired for a period of 1-60 minutes. In evoked response studies, averaging is often employed to reduce the number of data samples to less 10,000. However, analysis of continuous raw data is becoming more and common to reveal fine details of brain dynamics and to compute the statistics of the current estimates. Second, an accurate forward field and potential calculation requires numerical solution of the Maxwell's equations using either the Boundary-Element Method (BEM), the Finite-Element Method (FEM), or the Finite- Difference Method (FDM) and has to be repeated for hundreds or thousands of elementary sources.

Location: Hughes Aircraft Electrical Engineering Center (EEB) - 248

Audiences: Everyone Is Invited

Contact: Kaleena Richards