Competition between two sides of the brain makes it asymmetrical.

Byline: ANI

Washington, January 15 (ANI): A Wellcome Trust-funded study has shown that a competition between the two sides of the brain causes it to become asymmetrical, which is thought to be important to enable the two hemispheres to specialise and operate more efficiently.

The study on brain development in zebrafish is the first to cast light on the mechanisms that brings about the left-right asymmetry in the brains of most animals.

During the study, PhD student Jenny Regan and her colleagues in Professor Stephen Wilson's team at University College London (UCL) found that a protein called Fgf8 acts as a magnet to attract nerve cells to one side of the brain.

"Fgf8 is found in both sides of the brain, leading to a 'tug-of-war' competition between the two sides to attract the migrating group of nerve cells. This isn't a fair fight, however - Fgf8 on the left-hand side has an ally to help it win the battle," says Dr. Regan.

The researchers have also revealed that another protein called Nodal, present only on the left, teams up with Fgf8 to attract the group of nerve cells, thereby triggering cascade of events that lead to asymmetric development of the brain, with neurons on the left making different connections to those on the right.

According to them, the combined action of Fgf8 and Nodal ensures that when the asymmetry develops, it is usually in the same direction, which helps explain why there is consistent handedness between individuals.

Nodal is known to also play a role in other areas of the body where asymmetry occurs, such as the heart and positioning of internal organs.

Inhibiting it makes the competition fairer, and the group of nerve cells has an equal probability of migrating to the right or left side.

However, a bias in the direction of migration can be restored by adding extra Fgf8 to one side of the brain.

"Brain asymmetry is essential for proper brain function. It allows the two sides of the brain to become specialised, increasing its processing capacity and avoiding situations of conflict where both sides of the brain try to take charge," says Professor Wilson.

"For example, faced with a predator, an animal would not want both sides of the brain to try to drive the escape as this might lead to conflict over which direction to turn. Instead, the animal might keep watch more with one eye (and consequently one half of the brain) and so each side of the brain might be dominant for particular activities," the researcher adds.

Studies conducted in the past have already demonstrated that rearing chickens in the dark makes their brains less asymmetric. The chicks can still peck for food and watch out for predators if they do one of the tasks at a time, but they are less efficient in doing both tasks together as compared to fully asymmetric animals in which one eye specialises for one task and the other eye for the other task.

In humans, people with schizophrenia have disrupted brain asymmetries, it is not clear to date whether there is a causal link between the asymmetry and schizophrenia.

"The direction and handedness that brain asymmetry takes is not critical for survival, but the strong bias towards one direction may be to ensure that all members of a population have consistent behaviours. This may be very important for social animals, such as humans and schooling fish," says Professor Wilson.

A research article on this study has been published in the journal Neuron. (ANI)

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