Dear Renzo

That's interesting. I imagine one possible "null" explanation would be that perhaps those differences are just random (e.g. some connection may be a bit below a p<.05 threshold in one case and a bit above that same threshold in another case). On the other hand, one "non-random" possibility would be that those variations are associated with "novelty" or similar effects at the beginning of the scanner, which can cause consistent fluctuations in connectivity when comparing the beginning and the end of a scan across subjects. Comparing connectivity estimates obtained from different window lenghts/durations can also unfortunatley confound the results interpretation a bit, as larger temporal windows can be expected to produce increased sensitivity for "static" FC estimates, but also decreased resolution to identify potential "transient" FC states. 

Hope this helps

Alfonso

Originally posted by Renzo Torrecuso:

Dear Alfonso and CONN experts,

I cutted my .nii files so that they had progressively more volumes (e.g. the original has 300 and I analysed ROI2ROI from .nii sectioned in 100, 150, 200 and 250 volumes).

For my surprise, some ROI2ROI connections dissapeared with more volumes and appeared with less.

First I hipothesized that the reason why , say, a connection appeared with 150 volumes but not with 200, was that in 150 volumes there was more correlation between the time series and on the next 50 volumes this correlation fell. But this doesnt seem likely to happen in all 30 individuals, right?

Would you have any theoretical insight on why in more volumes some connections may vanish?

Thanks a lot,

Cheers

Renzo