Animals also have asymmetrical brains

Whether in a small flower or in the solar system, the beauty of geometry rules in nature.

Isaac Newton thought that this was evidence of the existence of God and highlighted the perfect symmetry of the human body.

However, for living things, having symmetry is just as important as being able to break it.

On June 15, 1865, Pierre Paul Broca presented to the Paris Anthropology Society the work he had carried out during the last five years.

In his medical profession, he had analyzed the brains of several patients who, when alive, showed speech deficits.

He discovered that most of them had damaged an area in the left frontal lobe and concluded his speech with the famous phrase: "We speak with the left hemisphere."

With a stroke of the pen, he overturned the scientific dogma that all healthy organs were symmetrical and ushered in the scientific investigations known as brain laterality.

Ironically, the special or divine character of our symmetry was reversed, and left-versus-right hemisphere differences became flagships of our superior status as a species.

Broca himself argued that the asymmetry was the result of education and civilization, a consequence of having overcome animal existence, and even some scientists were quick to affirm that the brain of men was more asymmetrical than that of women.

Descartes had proposed the pineal gland of the brain as the seat of the soul, but, by the end of the 19th century, it seemed that it was our left hemisphere that made us human.

These ideas were more a reflection of the prejudices of the time than of neurological evidence.

Since language is an exclusively human characteristic, it was easy to assume that the rest of the animals had symmetrical brains.

Thus, the hypotheses that considered brain laterality as the result of a single gene mutation that occurred in the Homo sapiens lineage dominated.

It took more than a century after Broca's discovery for science to realize that brain asymmetry is a widespread feature in the animal kingdom.

In 1979, the neuroscientist Lesley Rogers published the first article that provided definitive evidence that other animals also had cerebral laterality, specifically the chicken.

During the last three days of incubation in the egg, the chicks adopt a position in which one eye is covered by the body and the other is exposed to light filtering through the shell.

As the information from each eye is processed in a different hemisphere, this development causes asymmetries in the brain.

For example, chickens use the right eye to search for food and the left to detect predators, but when eggs are subjected to total darkness, the cerebral hemispheres do not specialize and chickens lack this ability.

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We now know that even a small nematode worm (

), with just 302 neurons, has functional asymmetries in its nervous system.

A neuron located on the left side of the body triggers the worm to move forward, while another neuron located symmetrically on the opposite side triggers a change of direction.

Other invertebrates, especially the bee and the vinegar fly, have also been extensively studied due to their cerebral lateralization.

Rogers discovered in 2013 that honey bees use their right antenna to recognize members of their group, but are unable to do so with their left.

Animals don't have brains as developed as ours because it wouldn't be profitable for them from an energetic point of view, but why wouldn't they specialize their hemispheres?

The ubiquity of lateralization in animals suggests that, regardless of brain size, dividing functions between the two sides of the brain provides important adaptive advantages.

Among other things, it allows us to have a greater cognitive space to carry out more types of processing, or to be able to combine tasks, as in the case of chickens with food and predators.

There is abundant evidence that lateralization of the brain improves the cognitive capacity of animals.

For example, science has wanted to check on several occasions if some fish (

) are good at numbers, usually by subjecting them to tests in which they have to discriminate between more or less numerous groups of objects.

Interestingly, there are large differences between individuals.

While some fish pass all the tests, others usually fail.

The explanation for this diversity lies in the degree of cerebral lateralization that each one has.

Faced with a predator, there are fish that almost always turn to the right to flee, others to the left, and others that show no preference.

Well, it is the latter who fail the numerical tests.

Emotion processing is also asymmetric in animals.

Broadly speaking, the left hemisphere tends to dominate in positive emotions and the right hemisphere in negative ones.

In 2017, three researchers decided to study whether it was possible to obtain information about the mood of a horse by noticing the leg they used to start walking.

They put a carrot in a wooden box with a lid located 10 meters from the horse.

Sometimes the box was offset 4 meters to the right and the horse could easily open it, while other times it was offset 4 meters to the left and was tightly closed so the horses could not get the carrot.

Next, they put a new box in the center to test if the horse approached it.

They repeated this procedure with 17 subjects and, depending on whether they were motivated to go to the ambiguous box in the center, the scientists categorized the horses between optimists and pessimists.

They also analyzed the leg with which each horse normally began to walk.

The study confirmed that the optimistic horses used their right side much more than the pessimistic ones, which makes sense considering that the right side of the body is connected to the left hemisphere, which is the one that processes positive emotions.

There is also evidence that several domestic animals are more frightened when they see an unknown human with their right eye than when they see it with their left eye, since the information from the latter reaches the right hemisphere, specialized in processing new stimuli.

In the end, recognizing the cerebral laterality of animals is allowing us to better understand their emotions and, therefore, improve the quality of the relationship we establish with them.

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