PSDs spatial smoothing [2024] does not look smooth

Hello everyone,

I want to compare PSDs maps computed at the source level across several subjects. To do so, I project each individual PSD file on a common anatomy, average them and then apply spatial smoothing. I used spatial smoothing [2024] and the result looks less smooth than the original file. Below is an example with the original image on top and the "smoothed" one on bottom. I used spatial smoothing [2024], FWHM 10 mm and geodesic distance. I tried applying spatial smoothing before averaging and it leads to the same result.

Thanks for your help

Thanks Pauline -- I will let others reply re: the outcome of spatial smoothing (@edelaire ?) but you want to make sure you first project individual data, then smooth each individual map, before averaging maps across participants (I understand your tried both, leading to the same outcome, but my comment is wrt the ordering of your pipeline). The rationale for smoothing is to reduce inter-individual spatial variability after projection on template anatomy across individuals.

Hi @pamrouche, I have ran smoothing on projected PSDs, and things look alright.

Do you observe the same behaviour by smoothing the first PSD files in subject space, before computing relative (power in physical units U^2/Hz)?

Hi everyone,
Thank you Sylvain for your insights.
@Raymundo.Cassani thanks, indeed when smoothing first, then computing the relative power and projecting on default anatomy I observe a smoothing effect (top figure). However by smoothing before the projection I fear that it will not be effective to reduce inter-individual spatial variability as Sylvain said.

That was to discard some troubles with the smoothing execution.

For sake of testing, can you project the sources, and compute PSD on the projected sources?