Dear all,

I have general questions regarding bandpassing via "-regress_bandpass x y" in AFNI proc. I know that AFNI recommends to avoid bandpassing, but isn't it required in some cases (see below)?

1. Does the polort option "-regress_polort x" automatically take care of noise sources like slow scanner drift/noise etc.? Does this option function a bit like a high-pass filter, so that noise below ~0.007 Hz or below ~0.01 Hz is removed? Or: does another option take care of that, if so, which option would it be?

2. I am currently computing the temporal autocorrelation of the time-series. For example, I am determining at which sampling point (TR) the autocorrelation of the signal drops to or below 0. My TR is 2.16s and hence the Nyquist frequency is 0.23 Hz. Applying "-regress_bandpass 0.01 0.23" results in much shorter autocorrelation results compared to results where AFNI proc ran without bandpassing. What would be the more appropriate option here, bandpassing in AFNI proc or no bandpassing?