We are analyzing some data using MELODIC (temporal concatenation option)
that we did not collect ourselves and are baffled by the number of MELODIC
components that result (over 100). This is much higher than we've seen in
our own data and are wondering what the causes might be, or if it is within
the bounds of what we should expect. There are 492 TRs per scan, with almost
40 scans included in the original analysis (each participant contributed one
or two scans). Many of the MELODIC components show very high values for one
person or scan and very low values for the rest of the participants. We have
tried a variety of things and everything just ends up leading to even more
components:
1. We went back and ran MELODIC for each individual separately and denoised
their data by removing components that appeared to be motion or other
artifacts, then reran the overall set. This did not appear to improve matters.
2. Because it looked like one person in particular was driving many of the
components that showed a large effect size for one person and not the rest,
we reran the analysis without that person. That led to a result with even
more components, many driven by another person. We excluded that person, and
got a result with even more components.
3. We added 10 mm to the spatial smoothing. That was also no help.
Does this suggest a problematic dataset or is there something we might be
doing incorrectly?
Many thanks,
Mara
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