Macroscale Connectivity in the Octopus brain

Comparative studies support the existence of functional analogies between given areas in the octopus and mammalian brains. Despite marked phylogenetic distance, the central nervous system of cephalopod mollusks is characterized by a complex network of anatomically interconnected and interacting neuronal populations. Previous studies provide a thorough description of the octopus neural network through neuronal tracing of axonal projections, offering a unique opportunity to systematically examine the brain network architecture. Here, we chart the topological organization of Octopus vulgaris neural network including information on the macroscale interregional pathways between 32 cortical and subcortical regions as provided by a high-quality historical dataset. We found more than 350 main neural connections (afferent, efferent) encompassing the three masses of octopus brain (supra-, sub-oesophageal masses, optic lobes). The octopus brain network possesses multiple nonrandom features promoting segregation and integration, including near-minimal path length, multiscale community structure, hubs, small-world features, and motif composition. Taken together, these attributes support an association between network architecture and function and are consistent with studies in a range of other species, suggesting the existence of a set of universal organizational principles across phylogeny. These findings expand our understanding of neuronal structures by highlighting brain regions that had previously received less attention.