Dear Justine,
I don't think the brain necessarily behaves by region only - why would your blob not cover two (or more) lobes?
Jonathan, Christian and Swann have made valid points, in particular about the reference (i.e. either the individual subject in the case of an individual analysis, or population-based templates (greyscale averages) or atlases (labels) in the case of group analyses).
The devil's advocate could argue that your blob is neither in the insula nor in the parietal or temporal lobe, but in the sylvian fissure... Can you exclude atrophy as an explanation for your result? Again, comparing against the average of your subjects in this particular analysis may help.
With best wishes,
Alexander
-----------------------------
Alexander Hammers, MD PhD
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National Hospital for Neurology and Neurosurgery/ Institute of Neurology, University College London, UK
Am 3 nov. 2011 um 01:00 schrieb Jonathan Peelle:
> Dear Justine,
>
>> I have a conundrum with my DARTEL-VBM data.
>> I have this region showing a difference - see image attached. But this
>> single blob traverses two lobes: temporal and parietal. (It also follows
>> the border of the insula but does not overlay it.)
>> The question arises - what is the most likely explanation?
>> - there is a single blob in one of the regions, but there is some inaccuracy
>> involved in relating this to the canonical T1. If so how to deal with this?
>> - there are 2 blobs in 2 regions, which (either coincidentally or not) are
>> contiguous
>
> The suggestion of looking at your results on a template other than a
> single-subject template is a good one. I would suggest both the gray
> matter template generated by DARTEL (normalized to MNI space, assuming
> that your analysis was conducted in MNI space), and also perhaps an
> average structural image of all of the subjects. That may give you a
> slightly more accurate idea of the spatial resolution/location of your
> results.
>
> Also, as you no doubt know, smoothing can also contribute to putting
> results outside of what is obviously gray matter.
>
> (If this was an fMRI result I would also suggest looking at the
> location of peaks in single-subject data, but that doesn't make sense
> for a VBM study.)
>
> Finally, you can use a probabilistic atlas to identify where the peak
> lies, or where the cluster spans (XX% of the cluster lies in region 1,
> XX% in region 2). Such probabilistic atlases include the SPM Anatomy
> Toolbox (though I'm not sure if it covers the region you are
> interested in), or atlases from Alexander Hammers (you can search
> previous posts by him to find out more). The atlas-based approach may
> not give you a single answer, but it's a way of quantifying the
> options and being objective about your anatomical localization (though
> personally I think this should come after having a closer look at the
> templates—e.g. tedious anatomy, and then probabilistic atlases).
>
> All of that being said, I don't know if there is a good way to tell
> between the two possibilities that you list. If you have a result
> that is statistically significant, it is certainly appropriate to
> report it; as far as the interpretation, I think being straightforward
> about the level of (un)certainty is the best way to go. Though,
> hopefully some of these other suggestions will clear things up.
>
> Hope this helps!
>
> Best regards,
>
> Jonathan
>
> --
> Dr. Jonathan Peelle
> Department of Neurology
> University of Pennsylvania
> 3 West Gates
> 3400 Spruce Street
> Philadelphia, PA 19104
> USA
> http://jonathanpeelle.net/
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