# Is there a difference between cosine regressors(cosine_XX) calculated with aCompcor than tCompcor?

In fMRIPrep Principal components are estimated after preprocessed BOLD time-series (non-steady-state volumes are censored) and high-pass filtering thepreprocessed BOLD time-series (using a discrete cosine filter with
128s cut-off) for the two CompCor variants: temporal (tCompCor)
and anatomical (aCompCor).

Based on the fMRIPrep code they are concatenating cosine_XX from tCompcor and not from aCompcor. Is the cosine_XX regressors independent of whether they are computed by aCompcor or tCompcor?

Thanks

Hi,

Cosine regressors are not computed by any compxor method. The cosine filter simply acts as a high-pass filter (128 seconds), and it is applied before any compcor. You should use the cosine regressors in your GLM modeling if you use either compcor method.

Best,
Steven

1 Like