Brain Asymmetry Shapes Direction of Mental Number Line in Early Life
The lateralization of the brain, where the left and right hemispheres specialize in different functions, has been found to underlie the development of a left-to-right mental number line in newborn chicks. This groundbreaking study, published in the prestigious journal eLife, has been described as fundamental and compelling by the editors. The results of this research are expected to be of significant interest to scientists studying numerical cognition, brain lateralization, and cognitive brain development.
Traditionally, the mental number line, which represents numbers arranged from left to right or vice versa, was believed to develop through cultural experiences such as reading and writing direction. However, recent studies have shown evidence of a left-to-right mental number line in young infants and animals, challenging the notion that this spatial-numerical association is solely a product of cultural influences.
Brain lateralization, also known as hemispheric specialization, refers to the functional differences between the two hemispheres of the brain. Lead author Rosa Rugani, a Professor at the University of Padua, Italy, explains that embryonic light exposure can induce brain lateralization in domestic chicks, enhancing their spatial-numerical abilities and their tendency to count from left to right. The study provides direct evidence that brain lateralization is essential for the emergence of left-to-right spatial-numerical associations.
In a series of experiments, 100 chick eggs were incubated, with half exposed to light to promote brain lateralization and half kept in the dark. The chicks were then trained to locate food hidden behind specific bottle caps, with the results showing a clear preference for selecting the fourth cap from the left for strongly lateralized chicks. When the spatial cues were made unreliable, neither group showed a directional preference, highlighting the importance of brain lateralization in integrating spatial and numerical cues.
The researchers also found that when chicks used only their left eye (engaging the right hemisphere), they tended to choose the fourth cap from the left more frequently, while using only their right eye (engaging the left hemisphere) led them to select the fourth cap from the right. This further supported the role of brain lateralization in spatial-numerical associations.
The study concludes that brain lateralization, established through light exposure during embryonic development, is necessary for integrating spatial and numerical cues, ultimately boosting cognitive performance. The findings have implications for understanding the biological basis of numerical thinking and how early sensory experiences can influence cognitive outcomes later in life.
This research sheds new light on the developmental origins of numerical reasoning and highlights the potential impact of atypical brain organization on cognitive abilities. By uncovering the role of brain lateralization in shaping numerical thinking, this study paves the way for further investigations into the interplay between biology and cognition.
For more information, the study titled “Prenatal light exposure affects number sense and the mental number line in young domestic chicks” can be accessed in eLife (DOI: 10.7554/eLife.106356.3).
Journal information: eLife
