Left or right? The brain division determines how we map the numbers

Summary: A study in newborn chicks shows that brain lateralization is essential for the development of a large mental line from left to right. The chicks with heavily lateralized brains constantly mape numbers from left to right, while the weakly lateralized chicks did not show this pattern.

The findings provide the first direct evidence that lateralization promotes spatial -numeric associations, suggesting that our sense of numbers can be biologically based instead of purely cultural. This research deepens our understanding of cognitive development and could shed light on why numerical reasoning differs among people.

Key facts

Direct evidence: The lateralization of the brain is necessary for the numerical mapping from left to right in chicks. Light exposure effect: Exposure to augmented embryonic light lateralization and numerical-spatial performance improved.

Source: Elife

The lateralization of the brain, the trend of the left hemispheres and right to specialize in different functions, underlies the development of a mental numerical line from left to right, according to a study in newborn chicks.

The editors describe the study, published as a reviewed predimpression in Elife and that appears today as the final version, is fundamental. They say that the evidence presented is convincing and that the results will be of interest to researchers studying numerical cognition, brain lateralization and cognitive brain development more widely.

Many people intuitively think of the numbers arranged along a mental line, whether it extends from left to right, with smaller numbers to the left and larger to the right, or vice versa. It is believed that this representation, often called mental number line, is developed through cultural experience, especially through the reading and writing address.

However, research has shown evidence of a mental numerical line from left to right in babies and young animals, challenging this assumption and suggesting that this spatial-numical association can have biological roots.

Cerebral lateralization, also known as hemispheric specialization, refers to the idea that the two brain hemispheres are functionally different and have specialized roles in various cognitive processes.

“Exposure to embryonic light induces brain lateralization in domestic chicks and improves their numerical space skills and their tendency to” count “from left to right,” explains the main author Rosa Ragani, a professor in the Department of General Psychology, University of Padua, Italy.

“Although several models have proposed that the mental numerical line originates in brain lateralization, direct evidence has been lacking. Our study provides this evidence, which shows that lateralization is essential for the appearance of spatial associations from left to right.”

In domestic chicks, it is known that exposure to light during embryonic development promotes brain lateralization. Therefore, Rugani and his colleagues incubated 100 chick eggs, half exposed to light and half in the dark. This produced a group of strongly lateralized chicks and a weakly lateralized group of chicks.

After hatching, the chicks were trained to locate hidden foods behind the fourth lid of the bottle in a vertical row of 10 identical tapas. Once they learned this task, the team rotated the variety of feeders in 90 degrees to be horizontal and tested if the chicks would look for food in the fourth lid from the left or the right. Both limits constituted a plausible option, allowing researchers to observe any natural directional preference.

The strongly lateralized chicks showed a clear preference to select the fourth lid from the left, which suggests a mapping of numbers from left to right. In contrast, weakly lateralized chicks showed no consistent directional preference, randomly selecting between the two tapas.

Then, the researchers repeated this test while covering the left or right eye of the chicks. Because each eye mainly sends signals to the opposite hemisphere of the brain, this allowed the equipment to determine which hemisphere was processing information during the experiment.

When the chicks used only their left eye (involving the right hemisphere), those with heavily lateralized brains chose the fourth lid on the left more frequently, reinforcing the role of the right hemisphere in the integration of spatial and numerical signals. When these same chicks used only their right eye (involving the left hemisphere), they tended to choose the fourth lid on the right.

Weakly lateralized chicks could not solve the task in both monocular conditions. This suggests that brain lateralization, established through light exposure during the last days of embryonic development, is essential to integrate spatial and numerical signals, and increases cognitive performance.

In a monitoring experiment, the researchers proved how chicks would work if the spatial signals became unreliable. They changed the space between the tapas so that the physical position of the fourth lid will vary, which means that the chicks could only depend on the ordinal (numerical) information, not the spatial design, to locate the food. Under these conditions, neither the chicks strongly or weakly lateralized showed a directional preference.

“For the first time, we show that brain lateralization is not only related to the mental numerical line, it is necessary for it,” says Ragani.

“This finding brings strong experimental support to the idea that our sense of number and space is based biologically, but made up of the interaction of an individual with the environment.”

The authors suggest that a natural scanning pattern from left to right can have evolutionary advantages for chicks. For example, when feeding, you can allow them to efficiently locate and quantify food sources without overlooking areas.

“Our work shows that lateralized brain function plays a key role in the configuration in the way animals possibly include humans, think of numbers,” says Senior author Lucia Regolin, professor of the Department of General Psychology at the University of Padua.

“Understanding the biological basis of numerical thought can help us identify why certain cognitive skills arise when they do so in development and why they could be altered in people with an organization of the atypical brain.

“This research opens the door to other studies on the origins of the development of numerical reasoning and how early sensory experiences can influence subsequent cognitive results.”

About this research and neuroscience news

Author: Emily Packer
Source: Elife
Contact: Emily Packer – Elife
Image: The image is accredited to Neuroscience News

Original research: open access.
“Exposure to prenatal light affects the meaning of the number and the mental numerical line in young domestic chicks” by Rosa Rugani et al. elegant

Abstract

Exposure to prenatal light affects the meaning of the number and the mental numerical line in young domestic chicks

Humans order numerous throughout a mental numerical line from left to right (MNL), traditionally considered culturally rooted. However, some birth species show spatial-numeric associations (SNA), which suggests neuronal origins.

Several accounts link SNA to the lateralization of the brain but lack evidence. We investigate the effects of lateralization of the brain in numerical spatialization in 100 newborn domestic chicks.

In Ovo, exposure to light produced strongly lateralized brains in half of the chicks and weakly lateralized in the other half.

Chicks learned to select the fourth article in a sagital matrix. In the test, the matrix was turned 90 °, with the elements of the 4th left and right right.

The strongly lateralized chickens surpassed the weak weaknesses when ordinal and spatial signals were reliable (experiment 1), but not with unreliable spatial signs (experiment 2).

In addition, only strongly lateralized chicks showed directionality from left to right, which suggests the key role of the right hemisphere in the integration of spatial and numerical signals.

We show that brain lateralization is essential to develop an SNA oriented from left to right.