Does nilearn model the difference of means between runs?

1

I have multiple runs data for one task. Of course I want to use all the data to execute 1st level analysis.

I referenced this tutorial:
9.5.8. Simple example of two-session fMRI model fitting
https://nilearn.github.io/auto_examples/04_glm_first_level/plot_fiac_analysis.html

I saw the design matrix and found the design matrixs in this tutorial don’t model the run effect comparing with SPM design matrixs.

Just a example:
Nilearn:

image
image280×712 14 KB

SPM by Nipype:
111
1111735×1825 105 KB

Do I need add it into design matrix by myself? Or it is contained by fixed effect model?

For my unstanding, if i model the difference of mean between different runs, it will be a mixed effect model?

Am I understanding this correctly?

2

In Nilearn, the data from different runs are fit independently, and a fixed-effects analysis is run later. So, there is no need (and actually no way) to model session effects.
Does that answer your question ?
Best,

1 Like
3

@bthirion in your opinion, is there any advantage/disadvantage in modelling the different runs independently as opposed to modelling session effects in the same design matrix? Is there a rationale for the latter procedure?

4

The should not have a large effect on the results.

  • In terms of computation, having an aggregated model makes the fit more costly, and hence is suboptimal computationally.
  • On the other hand, you may estimate noise autocorrelation slightly better (but SPM12 is biased anyhow IIRC), and this is secondary anyhow.
    Best,
1 Like