Symmetrical brains can be an advantage

Oct 01, 2009 by Lin Edwards weblog
Girardinus falcatus. Image credit: eoldal.hu

(PhysOrg.com) -- Many studies have found widespread asymmetry in the brains of different species, including humans, and most have assumed asymmetry is advantageous. A new paper, published in the Proceedings of the Royal Society B, suggests it is not always an advantage, at least for one species of fish.

Many species have divided or asymmetrical brains with different functions in the two hemispheres, a phenomenon known as lateralization. Recent studies in primates, and birds have found that lateralized brains are common, but in fish and birds there is a wide range in the degree of lateralization within the species.

Studies on parrots have found that birds with more lateralized brains were more easily able to find food, but a group of scientists in Italy decided to find out if there were costs associated with lateralization as well as benefits.

The scientists, led by Marco Dadda of the University of Padua, spent four years breeding a known to have a lateralized brain, the goldbelly topminnow (Girardinus falcatus). The fish were divided into three groups according to the dominant sides of their brains. This was determined by observing which way the fish turned when escaping a predator. Those turning right 80% of the time were classified as right eye/left brain dominant, those turning left were left eye/right dominant, and those with no preference were classified as non-lateralized.

After classifying the fish, the scientists did a number of experiments to see if lateralization was beneficial or otherwise. In one experiment the fish were allowed to choose between two shoals of other minnows. Each shoal could be seen by only the right or left eye. The researchers reasoned that the best chance of survival for a fish such as the minnow is to belong to a large shoal of similar sized fish so the individual does not stand out from the crowd and draw the attention of predators.

The researchers found the non-lateralized fish picked the most advantageous shoal 60% of the time, but the lateralized fish chose to join the most advantageous shoal only 34% of the time, and more often preferred the shoal they saw with their dominant eye.

The findings suggest the non-lateralized fish were better able to judge information they received from both eyes, while the lateralized fish favored their dominant side. This means there is a trade-off between the advantages and disadvantages of lateralization. In some situations symmetrical brains that can process the information from both eyes equally are an advantage.

More information: The costs of hemispheric specialization in a fish, , doi: 10.1098/rspb.2009.1406

© 2009 PhysOrg.com

Explore further: Warning coloration paved the way for louder, more complex calls in certain species of poisonous frogs

add to favorites email to friend print save as pdf

Related Stories

How to Grow a Bigger Brain

Mar 06, 2006

Hatchery-reared steelhead trout show increased growth of some parts of the brain when small stones are scattered on the bottom of their tank, according to a new study by researchers at UC Davis. The brains ...

New species of Antarctic fish discovered

Dec 19, 2006

U.S. scientists have found a new species of Antarctic fish that are about 13-inches long, thrive in the cold and have an interorbital pit with two openings.

Study reveals secret sex life of fish

Feb 22, 2006

Scientists have long thought of deep-sea pelagic fish as nomadic wanderers, but now they suspect the fish may be meeting at ridges or seamounts to spawn.

Recommended for you

Cat dentals fill you with dread?

23 hours ago

A survey published this year found that over 50% of final year veterinary students in the UK do not feel confident either in discussing orodental problems with clients or in performing a detailed examination of the oral cavity ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

jsovine
not rated yet Oct 01, 2009
Are non-lateralized brains more prone to ambidexterity?
austux
not rated yet Oct 02, 2009
Are non-lateralized brains more prone to ambidexterity?

On a fish (no hands) how could one tell?
ElecMan08
Oct 03, 2009
This comment has been removed by a moderator.