Cytoarchitectonic mapping and probabilistic atlas of the human claustrum

2013 

Abstract Submission 

Navona Calarco¹, Olga Kedo², Sebastian Bludau², Christina Herold³, Kamil Uludag¹, Katrin Amunts²

¹University of Toronto, Toronto, Canada, ²Institute of Neuroscience and Medicine (INM-1), Forschungszentrum Jülich, Jülich, Germany, ³Heinrich Heine University, Düsseldorf, Germany

Navona Calarco  
University of Toronto
Toronto, Canada

Olga Kedo  
Institute of Neuroscience and Medicine (INM-1), Forschungszentrum Jülich
Jülich, Germany

Sebastian Bludau  
Institute of Neuroscience and Medicine (INM-1), Forschungszentrum Jülich
Jülich, Germany

Christina Herold  
Heinrich Heine University
Düsseldorf, Germany

Kamil Uludag  
University of Toronto
Toronto, Canada

Katrin Amunts  
Institute of Neuroscience and Medicine (INM-1), Forschungszentrum Jülich
Jülich, Germany

The claustrum is often described as the brain's most mysterious nucleus (Mathur, 2014). The mystery is a consequence of the claustrum's complex anatomy, which poses significant challenges to investigation via in vivo neuroimaging. The dorsal claustrum, which lies between the putamen and insular cortex above the level of the central insular sulcus, is remarkably thin, often submillimeter in its dorsomedial dimension. The ventral claustrum, approaching the lower circular insular sulcus and extending into the temporal lobe, consists of diffuse grey matter islands, fragmented by intersecting fascicles. At resolutions typical of in vivo MRI, the claustrum is difficult to discern from adjacent structures, and aspects of the ventral claustrum may evade detection altogether. Therefore, neuroimaging studies would greatly benefit from the development of a high-resolution, three-dimensional, probabilistic reference atlas, to better understand variations in individual anatomy, and support the investigation of claustral structure, connectivity and function in living humans. At present, no such reference exists.

Here, we create a cytoarchitectonic reference of the human claustrum. We mapped the claustrum as a singular structure in 10 postmortem brains (5 female, ages 37-85), on every 60th Merker-stained coronal section at 1 micron in-plane resolution (distance between sections = 1.2mm, total sections > 400). One of the examined brains is the BigBrain, allowing mapping across a continuous series of sections (Amunts et al., 2013). Using in-house software, we delineated the claustrum's borders according to apparent anatomy, informed by cytoarchitectonic criteria described by earlier studies (Brockhaus, 1940; Rae, 1954). Next, we reconstructed the claustrum in three-dimensions, and computed continuous probabilistic maps in the MNI-Colin27 and ICBM2009casym reference spaces, at 1mm isotropic resolution (Amunts et al., 2020).

The high-resolution delineation, in both hemispheres, and across multiple brains, allowed a thorough characterization of the claustrum's structure, whilst underscoring the inherent difficulty of claustral investigation in vivo. First, in keeping with earlier studies, we observed extraordinary heterogeneity in cytoarchitecture across the claustrum's extent [FIGURE 1A]. Second, we observed that the claustrum appears to directly abut the olfactory tubercles, amygdaloidal complex (Kedo et al., 2018), and the piriform cortex (Kedo et al., in preparation) [FIGURE 1B]. Third, we observed that, along the anterior-posterior axis, the anterior aspect of ventral claustrum extends medially above and then below the amygdaloid complex towards the piriform cortex [FIGURE 1C], surpassing what is denoted by other high-resolution atlases (Mai, Majtanik and Paxinos, 2015; Ding et al., 2017). More generally, our cytoarchitectonic mapping, as well as three-dimensional reconstruction and probabilistic maps, revealed a high degree of intersubject variability in the shape and extent of the ventral claustrum, especially its extension into the temporal lobe. Analyses in-progress investigate sex and hemispheric differences, and whether purported claustral subdivisions, located differently across existing atlases, have a clear basis in cytoarchitecture.

To the best of our knowledge, ours is the first high-resolution 3D cytoarchitectonic reference of the human claustrum, based on the analysis of multiple brains. Alongside advances in ultra-high field MRI, the maps hold significant potential to illuminate enduring questions of claustral structure-function relationships, by reducing misattribution of function to adjacent structures (and vice versa), and serving as seed regions for diffusion and functional connectivity studies. The probabilistic maps will be integrated into the growing number of subcortical cytoarchitectonic mappings in the Julich Brain Atlas (Amunts et al., 2020), accessible online, e.g. via the EBRAINS platform.

Segmentation and Parcellation ¹

Subcortical Structures

Brain Atlases ²

Atlasing

Cellular

Segmentation

Sub-Cortical