Neuromag coherence

Cristiano Micheli michelic72 at GMAIL.COM
Wed Jun 25 12:26:22 CEST 2008

Hi All
I checked the tutorials:
"Localizing oscillatory sources using beamformer techniques" and "Analysis
of corticomuscular coherence" and it seems that cortico-muscular coherence
calculations and dics have to do with sourceanalysis.m routine.
I managed to have it working after having calculated frequency power spectra
and cross-spectral densities as inputs for this function.
After i select the other inputs (head model, gradiometer's positions,
lambda) i have to set a frequency upon which to let the dics run (i
selected, like in the examples, the peak of maximal coherence spectra).
The result of the run is a 3D map of coherence or power activities for every
point inside the head grid and i used a scatter3.m to visualize it, not to
mess up with the co-registration of MRI images (the next step i will speak
I compared the result with a coherence topography calculated with CTF
software and i get an activation in the controlateral area with a clear
dipolar shape. 
Unfortunately i do not see an equivalent in the same position for the DICS
Reading the documentation i realised that it can be because of a biasing of
the spatial filter toward the center of the sphere. I recalculated the dics
with a baseline condition and after all i subtracted it from the task
activation, still the result is far away from being a localized source
activity, according to me. I also tried with different lambda but the result
is not localized.
How can i fix it?

Thanks in advance for the help


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