AFNI version info (`afni -ver`

): 23.1.02

Hello!

I am running 3dLMEr on my data and I am interested in looking at whether "symptom improvement" is significant in my fMRI data. We have 2 symptom scores per individual: from baseline and from endpoint. We had the participants complete a task with 2 within-subject conditions (PrevTrial and CurrTrial, both could be either incongruent or congruent; a total of 4 sub-briks per participant). I've been doing some digging and it seems like the most appropriate way to include a change in symptom scores in the model is to use 2 variables, one for baseline score and one for endpoint score on their own, rather than calculating the difference score between them (i.e. endpoint-baseline) and inputting that as its single variable. As I understand, using a difference score assumes that both baseline and endpoint will have equal and opposite signed coefficients, which we cannot assume. The baseline and endpoint scores in my model are the variables CAPS_wk0 and CAPS_wk12; we also have between-subjects variables for Motion and Sex as covariates of no interest.

Is there a way to look at whether the change in symptom scores is significant in my model? I tried to do this by setting CAPS_wk0 as -1 and CAPS_wk12 as +1 in a post-hoc test (see '-gltCode CAPS_change'). I was wondering if this was the appropriate way to code this contrast in my model? Or am I off base? When I looked at the results of the contrast, I was quite surprised as there were a lot of clusters that came up as significant (like 35 or something). When I look at CAPS_wk0 or CAPS_wk12 alone, there is only one significant cluster for each (both for the F-test and the -gltCode t-test that I specified in the first two -gltCode lines), so I suspect something is going awry here.

Thanks!

Ryann

```
3dLMEr -prefix Models_Apr11-2024/ModelCAPS_Apr11-2024 \
-jobs 10 \
-mask mask_epi_anat/group_mask_epi_anat_gm+tlrc \
-qVars 'CAPS_wk0,CAPS_wk12,Motion' \
-model 'CAPS_wk0+CAPS_wk12+PrevTrial*CurrTrial+Motion+Sex+(1|Subj)+(1|Subj:PrevTrial)+(1|Subj:CurrTrial)' \
-gltCode CAPS_wk0 'CAPS_wk0 :' \
-gltCode CAPS_wk12 'CAPS_wk12 :' \
-gltCode CAPS_change 'CAPS_wk0 : -1 CAPS_wk12 : 1' \
-gltCode con1 'PrevTrial : 1*incongruent CurrTrial : 1*congruent' \
-gltCode con2 'PrevTrial : 1*congruent CurrTrial : 1*congruent' \
-gltCode low 'PrevTrial : 1*congruent CurrTrial : 1*incongruent' \
-gltCode high 'PrevTrial : 1*incongruent CurrTrial : 1*incongruent' \
-gltCode inc-con 'CurrTrial : 1*incongruent -1*congruent' \
-gltCode low-high 'PrevTrial : 1*congruent -1*incongruent CurrTrial : 1*incongruent' \
-gltCode con1-con2 'PrevTrial : 1*incongruent -1*congruent CurrTrial : 1*congruent' \
-dataTable @datatable.txt
```