P-VS/RepSim: The RepSim Matlab tool is developed to perform Monte Carlo simulations of fMRI experiments. The resulting text file gives an idea of how likely it is, to have a false positive result repeated in j subjects out of a sample of N subjects. · GitHub

The RepSim toolbox is developed to perform Monte Carlo simulations of fMRI experiments. The resulting text file gives an idea of how likely it is, to have a false positive result repeated in n subjects out of a sample of N subjects.

The RepSim toolbox is created with the app designer in Matlab R2020b. The code to do the simulations is based on the AlphaSim tool as implemented in RESTplus v1.24 (http://restfmri.net/forum/). In order to work, SPM12 (https://www.fil.ion.ucl.ac.uk/spm/) should be installed.

The script performs a S simulatiosn of statistical maps for N subjects. For each stimulation an activation count map is created and a group analysis (t-test) is performed.

The activation count maps can be created using an exact threshold (no weighted threshold) or a weighted threshold. In case of the weighted threshold, the activation count is determined as

• 1 if p<=pthres
• exp(-(1/2)*((p-pthres)/width)^2) if p>pthres

The results are given in a tekst file:

• Number of subjects (n): a significant result is found in at least n out of N subjects
• Percentage of subjects: n given as percentage of N
• Frequency >=n: Number of times (in voxels) an overlap of a false positive result is seen in at least n subjects (summed over all simulations)
• Probability of >=n: Probability of having an overlap of a false positive result in at least n subjects
• Freq significant group: Number of voxels showing an overlap of a false positive result is seen in at least n subjects and a false positive group effect
• Probability significant group: Probability of having an overlap of a false positive result in at least n subjects and a false positive group effect
• Found in x simulations: Number of simulation in which an overlap of a false positive result in at least n subjects and a false positive group effect is seen in at least 1 voxel
• Mean freq per simulation: Mean number of voxels per simulation showing an overlap of a false positive result in at least n subjects and a false positive group effect
• SD freq per simulation: Standard deviation of the number of voxels per simulation showing an overlap of a false positive result in at least n subjects and a false positive group effect
• Max freq per simulation: Maximum number of voxels per simulation showing an overlap of a false positive result in at least n subjects and a false positive group effect

The 'Result_analysis' folder contains a SPM toolbox to create activation count maps (ACM) or weighted overlap maps (WOM) from real fMRI results. The whole 'Result_analysis' folder should be saved as a subfolder in the 'SPM12/toolbox' folder.