| Abstract No.: | A-G1198 |
| Country: | Canada |
| | |
| Title: | THE ANTERIOR INSULA: MORPHOLOGY, VARIABILITY AND DELINEATION OF BORDERS FROM THE ORBITOFRONTAL CORTEX |
| | |
| Authors/Affiliations: | 1 Jurgen Germann*; 1 Michael Petrides;
1 Cognitive Neuroscience Unit, MNI, McGill University, Montreal, QC, Canada.
|
| | |
| Content: | Objectives: The present study examined the morphological relationship between the anterior insula and the orbital and ventrolateral frontal cortex. The anterior insula and adjacent orbitofrontal region are functionally and anatomically diverse. Foci of anatomical and/or functional changes are frequently reported from this area and the same foci are sometimes described as being located in the insula or the adjacent frontal cortex. Our group in a recent study established that the insula proper finishes at the level of the apex and what is often wrongly described as anterior insula is in fact part of the orbitofrontal cortex: the accessory/transverse gyrus complex. These gyri can easily be identified by following their origin at the caudo-medial orbitofrontal cortex. However, even with this anterior border being defined, the morphology of the anterior insula remains variable: the gyral arrangement and location changes significantly between individuals. Thus the objective of this study was to investigate the morphology of the anterior insula and the adjacent orbitofrontal region providing a detailed description of the configuration and variability of sulci and gyri. Combined with the probabilistic maps computed the results can assist when localizing anatomical and/or functional changes in this region.
Materials and Methods: Anatomical magnetic resonance imaging (MRI) scans (1mm3) of 20 healthy subjects (10 female; average age = 25 ½ years, standard deviation = 5 years) were examined. The MRI scans were performed on a Philips Gyroscan 1.5-T system and transformed into the MNI standardized proportional stereotaxic space. All subjects were participants in the International Consortium for Brain Mapping (ICBM) project and were right-handed and had no history of neurological or psychiatric disorders. The anatomical structures of interest were identified and the voxels comprising each gyrus were marked manually using DISPLAY, an interactive 3-D imaging software package. Those markings were used to compute the probabilistic maps depicting the average location and variability of the different gyri in MNI space.
Results: The transverse gyrus originates from the most caudal part of the gyrus rectus, moves laterally and continuously into the accessory gyrus at the level of the apex. The accessory gyrus runs in a ventro-dorsal direction with its most dorsal portion submerged within the horizontal ramus. The transverse/accessory gyral complex provides a very reliable landmark. Within the anterior insula, the precentral gyrus can easily and reliably be identified. Two short gyri are usually found rostral to the precentral gyrus commonly referred to as gyrus brevis 1 and 2. These two gyri are highly variable with the sulcus separating them expressed very inconsistently. No separation between the gyri brevi could be found in 6 cases. The average location and variability in MNI standardized proportional stereotaxic space is described in combined probabilistic maps.
Conclusion: Reliable landmarks allow a separation of the different parts of the anterior insula and the adjacent orbitofrontal areas. Those landmarks combined with the probabilistic maps enable an exact localization of anatomical and/or functional changes in this region of the brain. |
| | |
| Back |
|
