A case study in connectomics: the history, mapping, and connectivity of the claustrum

Abstract

The claustrum seems to have been waiting for the science of connectomics. Due to its tiny size, the structure has remained remarkably difficult to study until modern technological and mathematical advancements like graph theory, connectomics, diffusion tensor imaging, HARDI, and excitotoxic lesioning. That does not mean, however, that early methods allowed researchers to assess micro-connectomics. In fact, the claustrum is such an enigma that the only things known for certain about it are its histology, and that it is extraordinarily well connected. In this literature review, we provide background details on the claustrum and the history of its study in the human and in other animal species. By providing an explanation of the neuroimaging and histology methods have been undertaken to study the claustrum thus far—and the conclusions these studies have drawn—we illustrate this example of how the shift from micro-connectomics to macro-connectomics advances the field of neuroscience and improves our capacity to understand the brain.

Psychedelics

“…Nevertheless, it is generally accepted today that the claustrum exhibits widely distributed reciprocal anatomic projections to virtually all regions of the cortex as well as to many subcortical structures, including the hippocampus, amygdala, and caudate nucleus. Substantial evidence now exists that the major target of claustral projections is the cortex, and that the major input to the claustrum comes from the cortex (see reviews by Smythies et al, 2012Smythies et al, , 2014Baizer et al, 2014;Mathur, 2014;Torgerson and Van Horn, 2014).…”

Topography of claustrum and insula projections to medial prefrontal and anterior cingulate cortices of the common marmoset (Callithrix jacchus)

“…Several recent hypotheses for claustrum function revolve around the highly networked connectivity of the claustrum, which has been demonstrated in humans (Torgerson and Van Horn, ) and rodents (Bota et al, ). Given the claustrum connectivity of prefrontal cortex in the cebus monkey, we recently proposed a novel hypothesis suggesting that the claustrum may play a role in switching between synchrony of task‐negative and task‐positive networks, such as the default mode and central executive or dorsal attention networks (Reser et al, ).…”

“…Both of these general ideas are underpinned by the widespread connectivity of the claustrum with the cerebral cortex. Indeed, the claustrum has been identified as one of the most highly connected regions of the human (Torgerson and Van Horn, 2014) and rodent (Bota et al, 2015) brain. Another attentionrelevant hypothesis regarding claustrum function revolves around coordination of sensory and motor areas between the cerebral hemispheres to facilitate exploratory activity (Smith et al, 2012;Smith and Alloway, 2014).…”

The functional connectivity of the human claustrum according to the Human Connectome Project database

“…Figure 1 shows in an axial view the anatomical location of the human claustrum. Research in humans using diffusion tensor imaging (DTI) have revealed cortical connections with the claustrum, which possesses projections to A) prefrontal cortex, BA 8,9,10,11,12 and 34;B) visual cortex,BA 17,18,19 and 39;C) sensoriomotor cortex, BA 7, 5, 1/2/3, 4, 6 and 8; and D) language areas BA 44, 45 and 31; as well as with orbitofrontal cortex, temporal cortex, basal ganglia and amygdala (Fernández-Miranda et al, 2008;Milardi et al, 2015;Torgerson and Van Horn, 2014). These results are consistent with the input-output of the claustrum to cortical areas previously reported in animal model studies (Goll et al, 2015).…”