-regress_polort DEGREE  : specify the polynomial degree of baseline

        e.g. -regress_polort 2
        default: 1 + floor(run_length / 150.0)

    3dDeconvolve models the baseline for each run separately, using
    Legendre polynomials (by default).  This option specifies the
    degree of polynomial.  Note that this will create DEGREE * NRUNS
    regressors.

    The default is computed from the length of a run, in seconds, as
    shown above.  For example, if each run were 320 seconds, then the
    default polort would be 3 (cubic).

  * It is also possible to use a high-pass filter to model baseline
    drift (using sinusoids).  Since sinusoids do not model quadratic
    drift well, one could consider using both, as in:

        -regress_polort 2         \
        -regress_bandpass 0.01 1

    Here, the sinusoids allow every frequency from 0.01 on up to pass
    (assuming the Nyquist frequency is <= 1), modeling the lower
    frequencies as regressors of no interest, along with 3 terms for
    polort 2.

  -regress_polort 2         \
  -regress_bandpass 0.01 1 \