Experts shed light on how evolution shaped eyesight

Experts shed light on how evolution shaped eyesight

A recent study shed some light on why evolutionarily ancient brain areas are important and how they affect people"s eyesight.

According to the report, published in the Journal of Neuroscience by experts from Ruhr-University Bochum in Germany, structures in the midbrain that developed early in evolution can be responsible for functions in newborns which in adults are taken over by the cerebral cortex.

Dr Claudia Distler-Hoffmann, from the university"s Department of General Zoology and Neurobiology, and Professor Klaus-Peter Hoffmann from the Department of Animal Physiology, say the evidence for this theory has been found in the visual system of monkeys.

They scientists studied a reflex that stabilises the image of a moving scene on the retina to prevent blur, the optokinetic nystagmus, and found that nuclei in the midbrain initially control this reflex and that signals from the cerebral cortex (neocortex) are only added later on.

In order to control sensorimotor functions such as eye movements, the adult brain is equipped with different areas in the neocortex, the evolutionarily youngest part of the cerebrum.

Professor Hoffmann explained that this raises the question why older subcortical structures in the brain have not lost the functions that can also be controlled by the neocortex.

Dr Distler-Hoffmann added: "The neocortex of primates is, however, not fully functional shortly after birth and therefore cannot control the optokinetic nystagmus. This is most probably also the case with people. Nevertheless, this reflex works directly after birth."

The experts examined what information controls the optokinetic nystagmus in the first weeks after birth and found that, during the first two weeks, the reflex is controlled by signals from the retina, which are transmitted to two nuclei in the midbrain, with the neocortex then adding its information and taking over during the first months of life.

The optokinetic reflex, which was studied by the researchers also at the behavioural level, is almost identical under the control of the midbrain and the neocortex and generally occurs when watching a moving scene.

First of all the eyes follow the passing scene, then they move quickly in the opposite direction back to their original position.

The specialists noted that, with this reflex, monkeys and humans build their slow eye tracking movements with which they keep an eye on moving objects.

"These findings from research with primates are important for recognizing and treating maldevelopments in the visual system of infants and young children at an early stage" Dr Distler-Hoffmann explained. 

by Martin Burns

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