The contrast will test for the difference in slope of thickness vs NPIDSEV effect between AD and MCI or AD and CN. if it is positive, it means that AD has a greater slope than MCI or CN. Note that this does not make a statement about the sign of the slopes so you can get a positive result when they are both negative as long as AD is less negative than MCI/CN.
On 7/14/2022 5:44 PM, Adriana Cannizzaro wrote:
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Hello Dr. Greve,
Please see attached the fsgd and contrast files. I would like to know how to interpret the max value and its directionnality. For example, for this contrast : *g2v1_CN_AD_NPIDSEV.area.lh.fwhm10_group-x-var_neg*, does the negative sign of the max demonstrate that the surface areas of the cuneus and inferior parietal are smaller for the CN group than the AD group as depression severity (NPIDSEV) increases ?
Thank you very much, Adriana
On Jul 10, 2022, at 5:56 PM, Douglas N. Greve dgreve@mgh.harvard.edu wrote:
I'm having problems following your narrative. Can you send the fsgd and contrast files?
On 7/4/2022 5:37 PM, Adriana Cannizzaro wrote:
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Hello Freesurfers,
We performed a whole-brain analysis using general linear model analysis with FreeSurfer mri_glmfit for neuropsychiatric symptoms (i.e: depression, etc) to assess their effect on brain’s cortical volume, thickness and area between groups (controls vs mild cognitive impairment, control vs Alzheimer, Alzheimer vs mild cognitive impairment).The severity score (level is either 1,2 or 3) of the neuropsychiatric symptoms was included as fixed factors, while MRI parameters (cortical volume, thickness and areas) were regarded as dependent variables.
Thus, these are two sets of results for group_x_var :
For reference : CN= Control group MCI= Mild cognitive impairment group AD: Alzheimer group NPIDSEV: Depression severity
*Contrast*
ClusterNo
Max
VtxMax
Size(mm^2)
TalX
TalY
TalZ
CWP
CWPLow
CWPHi
NVtxs
WghtVtx
Annot
Explanation
*g2v1_CN_AD_NPIDSEV.area.lh.fwhm10_group-x-var_neg*
is there a difference between the group VARiable slopes? contrast 0 0 1 -1. t-test with Group1>Group2 being positive. Note: this is an interaction between group and VARiable
1
-2.0763
158049
2847.57
-19.8
-63.8
12.5
0.0077
0.0066
0.0088
3957
-5537.87
cuneus
2
-2.4711
147091
2469.14
-35.3
-51.9
35
0.0205
0.0187
0.0223
5579
-7317.77
inferiorparietal
**
*g2v1_AD_MCI_NPIDSEV.volume.rh.fwhm10_group-x-var_pos*
is there a difference between the group VARiable slopes? contrast 0 0 1 -1. t-test with Group1>Group2 being positive. Note: this is an interaction between group and VARiable
**
1
2.2852
91120
1748.47
63.7
-39.7
-4.3
0.0054
0.0045
0.0063
3263
4658.91
middletemporal
We would like to have more information on the interpretation of these results. Specifically, we would like to know how to interpret the sign of the max coefficient in relation to the difference between the groups on the severity of depression/NPIDSEV and on the volume/area/thickness of the region of interest. Our interpretation for the first result for example was that the difference between the CN and MCI slopes is negative as depression severity increases, however this does not indicate the direction of the slopes regarding the area of the cuneus or the parietal inferior region. Is this correct?
Thank you very much for your help, Adriana Cannizzaro
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