I asked a neuroanatomist and insula expert on my campus about this a while back and this was his response:

"This is the region of the "limen insulae" that you will remember Dr. Heimer referring to often in the brain dissection course. The insula is defined as cortex which is covered by a lid of other cortical lobes, frontal, parietal and temporal. They all fold over except at the inferior frontal end where a little bit of the surface of otherwise insular cortex is not covered, and this little corner peeks out. This is the limeninsula which neighbors the olfactory cortex on the inferior surface of the frontal lobe and the medial surface of the temporal lobe, and is olfactory cortex itself. Since it is not covered over, it technically might not be considered really "insular" but it is obviously in continuity with, and not separated by any kind of sulcus or other landmark, from the rest of the insular covered cortex. So we are left with no secure boundary line between insular cortex and inferior frontal and medial temporal cortex in this corner. It looks like Freesurfer has decided to call it all insular, and with good functional reasons."

Cheers,

On Thu, Aug 7, 2014 at 3:32 PM, Bruce Fischl <fischl@nmr.mgh.harvard.edu> wrote:

Hi Mike

I'm not sure - I think the insula was an additional label that Ron Killiany added. I'll cc Ron to see if he has any insight. It certainly looks too medial to me.

I would also check on the white surface just to make sure that it's not a quirk of the inflation. If the aseg looks right we could certainly put together some simple auto-editing to correct this kind of thing

cheers
Bruce

On Thu, 7 Aug 2014, Harms, Michael wrote:

Hi,
An astute RA, while reviewing the aparc+aseg.mgz of brains processed with FS
5.3, noticed a fair number of instances, where the insula label "wraps
around" pretty medially, where she was expecting to see orbitofrontal as the
label. See attached jpg's for two examples shown on the inflated surface.
Since this is fairly common, I'm assuming that this isn't anything to be
concerned about, but just wanted to confirm.

Has this always been the behavior of the insula label, and we just didn't
notice it previously?

thanks,
-MH

--
Michael Harms, Ph.D.
-----------------------------------------------------------
Conte Center for the Neuroscience of Mental Disorders
Washington University School of Medicine
Department of Psychiatry, Box 8134
660 South Euclid Ave. Tel: 314-747-6173
St. Louis, MO 63110 Email: mharms@wustl.edu

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