BrainVoyager version: 22.4.6
Dataset used: Getting Started Guide data
It can be useful to define a region of interest based on a statistical map of task-related activations or resting-state connectivity patterns. This is for example the case if one wants to target regions that are relevant for particular cognitive or perceptual processes that do not follow precisely anatomical landmarks.
This document shows in a step by step example how to create functionally defined regions of interest in volume space (VOI).
To start, we open a VMR document, in this case the MNI-normalized dataset of sub-01.
Next, we need to compute a GLM or load a pre-computed GLM. In the current example, we link the sub-01_ses-04_task-blocked_run-01_bold_SCCTBL_3DMCTS_THPGLMF3c_MNI.vtc file and compute a single study GLM.
To identify brain regions that respond more to faces than to houses, we compute the contrast [Faces_LVF +1] + [Faces_CVF +1] + [Faces_RVF +1] ≠ [Houses_RVF -1] + [Houses_LVF -1] + [Houses_CVF -1] in the 'Overlay GLM Contrasts' dialog:
Based on this statistical map we can generate a subject-specific set of regions of interest that show a stronger response to faces than to houses. To do so, we can use the menu item 'Options -> Convert Map Clusters to VOI(s)'.
In the appearing dialog we can choose to create a single VOI from all supra-threshold voxels in the statistical map or we can choose to create one VOI per functional cluster. Especially for the latter option it is important to choose a reasonable cluster threshold to minimize the generation of VOIs based on small noise clusters.
The resulting set of subject-specific functional regions of interest can be saved by clicking on 'Save' in the 'Volumes-Of-Interest' dialog.
Alternatively, we can use the 'Volume Maps' dialog to convert all functional clusters in the statistical map to a single VOI. First, we need to move to the 'Volume Maps' dialog via the menu 'Analysis -> Overlay Volume Maps..'
Please uncheck the 'Trilinear Interpolation' option to see the functional resolution of the loaded statistical map, in the current example, 2x2x2 mm3:
In the 'Advanced' tab of the dialog we can choose to create one VOI per statistical map. Importantly, no cluster threshold is applied when converting the map to a region of interest - all supra-threshold voxels of the statistical map will be included in the resulting VOI.
Also here the resulting VOI can be saved to disk by clicking on 'Save' in the 'Volumes-of-Interest' dialog.