Shared features of connections between brain hemispheres likely originated in early mammalian ancestors, predating the evolution of the corpus callosum, a study suggests. The brain's left and right hemispheres are connected via a structure called the corpus callosum in placental mammals, or eutherians, and via a structure called the anterior commissure in pouched and egg-laying mammals, or marsupials and monotremes. However, whether the pattern of interhemispheric connections in eutherians arose through the evolution of the corpus callosum or instead reflects more ancient principles of mammalian brain organization remains unclear. Linda Richards, Rodrigo Suárez, and colleagues compared eutherian datasets with patterns of interhemispheric connections in the duckbilled platypus, a monotreme, and the fat-tailed dunnart, a marsupial. MRI of fixed dunnart and platypus brains revealed that interhemispheric nerve fibers are spatially arranged within the anterior commissure according to the 3D position of cortical areas, resembling patterns previously observed in the corpus callosum of eutherians. Circuit mapping experiments on dunnart brains revealed additional similarities with known features of the eutherian cortical connectome. According to the authors, the findings provide a framework for future studies on the evolution of vertebrate brain circuits.
Article #18-08262: "A pan-mammalian map of interhemispheric brain connections predates the evolution of the corpus callosum," by Rodrigo Suárez et al.
MEDIA CONTACT: Linda Richards, The University of Queensland, Brisbane, AUSTRALIA; tel: +61-7-3346-6355; e-mail: richards@uq.edu.au
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