The DTI connectivity of the human claustrum

Abstract

The origin, structure, and function of the claustrum, as well as its role in neural computation, have remained a mystery since its discovery in the 17th century. Assessing the in vivo connectivity of the claustrum may bring forth useful insights with relevance to model the overall functionality of the claustrum itself. Using structural and diffusion tensor neuroimaging in N = 100 healthy subjects, we found that the claustrum has the highest connectivity in the brain by regional volume. Network theoretical analyses revealed that (a) the claustrum is a primary contributor to global brain network architecture, and that (b) significant connectivity dependencies exist between the claustrum, frontal lobe, and cingulate regions. These results illustrate that the claustrum is ideally located within the human central nervous system (CNS) connectome to serve as the putative "gate keeper" of neural information for consciousness awareness. Our findings support and underscore prior theoretical contributions about the involvement of the claustrum in higher cognitive function and its relevance in devastating neurological disease.

Keywords: brain networks; claustrum; cognition; connectivity; consciousness; cortex; diffusion tensor imaging; graph theory; magnetic resonance imaging; neurology.

Figure 1

(A) In the human brain, the claustrum is a thin band of cells located medial to the insular cortex and lateral to the putamen. (B) Three‐dimensional models of the bilateral claustra were obtained from T₁‐weighted MPRAGE structural MRI image volumes. (C) White matter fiber tractography was performed and inter‐regional connectivity was computed by determining the relative proportion of extracted fibers initiated or terminated within the boundaries of each anatomical parcel. Here, fibers linking the claustrum to other brain regions are illustrated in an example subject. (D) These measures are aggregated into an M × M connectivity matrix, shown here as an image in which black refers to no or relatively low inter‐regional connectivity between region i and region j, varying to white reflecting a greater extent of region. (E) Regional morphometrics for the entire brain are represented as a circular “connectogram.” The measurements for each region are shown as “heat rings” including, from the outside inward, cortical thickness, regional volume, surface area, and connectivity density. The information contained in the computed connectivity matrix is used here to illustrate the pattern and strength of connections between brain regions. Line opacity is proportional to connection density, whereas color represents the average FA integrated along all pathways comprising that connection. Red is high average FA, green in medium average FA, and blue if low mean FA, according to the upper, middle, and lowest thirds of the FA distribution. Further information on connectogram construction and interpretation can be found in Irimia, Chambers et al. [2012b]. (F) The connectogram showing only those fiber pathways which eminate from or are connected to the left and/or right claustra. These fibers were subject to the graph theoretical analysis described in the body of the text.