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Volume 1, Number 2, pp. 18-22, 1999.    


 


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Reply to Comments Made by R. Grave
De Peralta Menendez and S. L. Gonzalez Andino

Roberto Domingo Pascual-Marqui


 

Figures

 

LORETA

Figure 1. Rows are horizontal tomographic slices through a unit radius spherical head. First row indicates the actual test sources and dipolar moment. Second to fourth rows show estimated LORETA current density for each field component (dipolar moments). Fifth row is strength of current density field. Test sources in (1a) and (1b) have unit strength. Note that the estimated deep source in (1a) is more blurred (about 17 times less amplitude) than the shallow source in (1b). LORETA can resolve both simultaneously active sources by increasing the strength of the deep source, as shown in (1c).

 

 

Minimum Norm

Non-regularized

Regularized

 

LORETA

Non-regularized

Regularized

Figure 2. LORETA and minimum norm images (non-regularized and regularized) corresponding to a test point source at Talairach coordinates (-3,-46,43). Noise was added to the scalp voltages (ratio of variances of signal to noise (SNR) equal to 10). Regularization was estimated via minimum cross-validation error. Anatomy is coded in black to white. Estimated current density in cortical grey matter is coded white (zero) to red (maximum). Location of maximum activity is indicated numerically and by black triangles on the coordinate axes. Estimated maximum strength is indicated numerically (single number following Talairach coordinates). Exact localization (with blurring) is achieved only with regularized LORETA. Other notation: (L=left; R=right; A=anterior; P=posterior).

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Official journal of the International Society for Bioelectromagnetism