The key facts

  • The hypothesis by Martin Wessendorf and Daniel Wang explains the crossed connection between hemispheres and sides of the body through the evolution of the visual system
  • The optic tectum (in mammals, the superior colliculi) already had a crossed organization, and the new cortex integrated into the ready-made scheme
  • The authors emphasize that this is an evolutionary explanation, not proof of the exact sequence of events

A hypothesis explaining the brain's crossed organization

The right half of the brain is connected mainly to the left side of the body, and the left half to the right. University of Minnesota neurobiologists Martin Wessendorf and Daniel Wang proposed an explanation of this principle through the evolutionary history of visual systems; their work was published in the journal Frontiers in Neuroanatomy. The hypothesis was reported by Gazeta.Ru.

The role of an ancient visual center

The starting point of the reasoning was vision: information about the right part of the visual field is transmitted to the opposite half of the brain, and information about the left part to the right. This principle of organizing visual pathways has been described in various vertebrates and is linked to an ancient visual center of the midbrain — the optic tectum, which in mammals corresponds to the superior colliculi.

How this could have become established

According to the researchers' hypothesis, the visual system with its crossed organization became the foundation around which evolution built new sensory and motor circuits: in the ancestors of mammals, many such pathways already crossed the midline of the nervous system. When the neocortex appeared, it was easier for it to integrate into the existing scheme, preserving the same principle of connections — a complete rewiring of the ancient circuits would have required additional changes to the 'wiring.' Thus, crossed control could have become established as a result of using an already existing architecture.

Limitations of the study

The authors and the publication emphasize that the work offers an evolutionary explanation but does not prove the exact sequence of events in the brains of animals that lived hundreds of millions of years ago. The article also recalls an earlier report in which scientists explained why the human brain is much larger than that of monkeys.