Hi,
We’re interested in brain activation vs inhibition which would be reflected in dipoles pointing in or out of the grey matter. It seems from the source localization (through constrained sLORETA) we are only provided with dipole orientations that reflect the surface structure of gyri vs sulci. Is there a way to get information about dipole direction relative to local grey matter?
Thank you.
Lin
Hello, I am not sure to understand your question, did you want to know if for example a dipole in occipital is negative or positive (so to remove the visualization or transformation into absolute values) to categorize these dipoles as inhibitor or excitator?
Hi Mawtyplant,
We want to know whether a brain area is inhibited or excited compared to baseline. It seems that the positive and negative values we obtain (after removing the transformation of brain scores into absolute values) blends together information regarding inhibition and excitation, and more so reflect the local surface structures of gyri vs sulci.
Thank you.
Lin
Still not sure to understand perectly but, if you right click to your brain figure, you can choose to show the values in absolute or relative value, you also got this option with the scout display in the time serie box (default is absolute but you can click in relative)
(you mean like a difference wave?)
To resolve inhibition vs excitation, as physiological processes, from source time series remains an open question. However, if you mean to better capture if a region is less activated than over baseline or another condition, for example, you may want to transform the source maps using z-score standardization of their absolute values, with respect to a time segment of interest. You can then interpret the sign of the resulting time series as the region being more (+), or less (-) “activated” than during the time segment of reference.
Hope this clarifies.
To add my two cents: with constrained orientation, the dipole orientation will always be perpendicular to the cortex, pointing out. And then you can look at negative vs positive values to see if it’s pointing in or out. However if I understand what you’re saying, you see negative and positive values that follow the geometry of the cortex. This is not unexpected since all inverse methods are not perfect and will spread in space. Imagine one dipole spreading into an extended patch of activity, but always keeping roughly the same absolute orientation. That orientation relative to the surface of the cortex will then be going in or out, depending on the cortex geometry.
So I don’t think you can interpret the orientation at each single point as being excitation or inhibition, but if there is a clear peak of activity, then maybe you can trust the orientation there.
Thank you, Sylvain. This might help. I will give it try.
Thank you, Marc. Correct, that is how we interpreted the signs as well. I was wondering if we were missing anything or if there is a way of telling apart inhibition vs excitation at single or small cluster of points. Perhaps we will take a look at peak activity.