Dear Prof. Zalesky,

We are running the NBS on task-based functional connectivity data and are facing several issues and maybe you can give us an advice on how to proceed.

1.) We conducted a one-sample t-test for each experimental contrast (e.g., one for the "alerting" contrast, one for "flanker" contrast etc.) and tried different thresholds, as recommended elsewhere in this forum, without getting any sign. results via the NBS.

I also read in the forum that it is a problem if we have more negative than positive values in the connectivity matrices (on a group level), if we want to apply a one-sample t-test, which is the case for all of our experimental conditions.

Just to be sure, is this really the case? Are our results therefore negatively affected by this mismatch of positive and negative connectivity values?


2.) Is it a "valid" approach to apply an a priori thresholding on the data, such as the "thresholding_absolute" from BCT to analyse positive and negative connections separately? Such as:

• threshold_absolute(flanker, 0) and threshold_absolute(flanker*-1, 0).

Because if we do so, we get significant results for both directions (positive and negative).

3.) To make things more complicated, our original data has directed (asymmetrical) connectivity matrices. Since the NBS is not suited for this kind of data we symmetrized our matrices beforehand.

4.) Do you have any other recommendations on how to work with connectivity matrices with more negative than positive connections while using the NBS and a one-sample t-test?


Many thanks in advance!

Best regards,

Ole