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Hi Bruce,

Thank you very much for your answer.

Kind regards, Rosie

On Sun, Nov 21, 2021 at 8:04 PM Fischl, Bruce BFISCHL@mgh.harvard.edu wrote:

Hi Rosie

It really depends on what your hypotheses are, but if you are covarying for age and gender in thickness you probably want to do so in an analysis of volume as well. The only real difference are (1) thickness doesn’t really need TBV covariation, and (2) thickness is a more localizable quantity than volume. Of course they are different neurobiologically as well, but from an analysis standpoint those are the two big differences

Bruce

*From:* freesurfer-bounces@nmr.mgh.harvard.edu < freesurfer-bounces@nmr.mgh.harvard.edu> *On Behalf Of *Rosalia Dacosta Aguayo *Sent:* Sunday, November 21, 2021 1:42 PM *To:* Freesurfer support list freesurfer@nmr.mgh.harvard.edu *Subject:* [Freesurfer] Basic question

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Dear Freesurfer team,

I know this is a basic question, but I would like to be sure before proceeding. Are those statements below right?

For cortical thickness, I should covariate for age and sex

For volume, I should covariate only for TBV

Thank you for your time and your patience.

Best wishes,

Rosie

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Hi KC

1. Volumes are typically correlated with TIV and so if you don’t care about TIV itself you probably want to include it as a nuisance variable (both cortical and subcortical) 2. Thickness does not show this correlation and typically does not need to be correlated. Surface area does, and so it should be included (possibly to the 2/3 power, perhaps someone else can comment on this?). Not sure about curvature, but I would assume not as least to first order

Cheers Bruce

From: freesurfer-bounces@nmr.mgh.harvard.edu freesurfer-bounces@nmr.mgh.harvard.edu On Behalf Of Koustav Chatterjee Sent: Monday, November 22, 2021 12:03 AM To: Freesurfer support list freesurfer@nmr.mgh.harvard.edu Subject: [Freesurfer] Requesting to clarify doubts on data analysis

External Email - Use Caution Dear FreeSurfer team,

I have a few questions to clarify the confusion regarding data analysis.

1. For each subject, is it recommended to normalize the raw volumetric data by total intracranial volume? If so, is it true only for volumes of subcortical structures or, both subcortical and cortical structures? 2. In the same way, do I suppose to normalize

* Different cortical thickness with mean cortical thickness * Cortical surface area with total surface area * Different cortical curvature with mean cortical curvature Thank you for your time and help.

Regards, KC