Neurobiological bases for quantity discrimination at birth: A study on newly-hatched domestic chicks

Numerical estimation abilities are extremely important in animals, as they allow for more efficient decision-making in ecological contexts regarding, for example, feeding, conflicts, or reproduction. Furthermore, in humans these abilities are fundamental as they constitute the foundation for subsequent formal mathematics learning during the school period. These abilities, which do not require a cultural symbolic system such as that provided by human language, appear to be supported by two different cognitive systems: the OTS (Object Tracking System), which is precise and operates with small quantities (approximately 3-4 units), and the ANS (Approximate Number System), which can also be used for larger quantities but is less precise, as it follows Weber's law. The present study aims to adapt a procedure previously validated in zebrafish (Danio rerio) to newly hatched domestic chicks (Gallus gallus), thus investigating the neurobiological bases of the ANS in a different phylogenetic group. The procedure combining the behavioral paradigm of habituation-dishabituation with molecular biology techniques (RT-qPCR). Separate groups of chicks were presented with sets of 3 or 9 dots during the first day of life exploiting the filial imprinting phenomenon for the habituation. The chicks were then tested for dishabituation with a change in number (from 3 to 9 or vice versa, keeping the area or perimeter constant based on the condition) or with a change in size (threefold increase or decrease in total area) while keeping numerosity unchanged. In the control group all conditions remained unchanged. The expression of Immediate Early Genes, as markers for neuronal activation, was quantified in the nucleus rotundus, entopallium, and Wulst, visual areas that we hypothesized to be involved in visual numerosity discrimination. Preliminary results showed significant main effects of brain area and dishabituation test, without significant interactions. However, no significant differences emerged in subsequent analyses between the different areas or between conditions. Nevertheless, a marginally significant difference between the two experimental conditions (balanced area and balanced perimeter) is noteworthy despite the halved sample size of these two groups compared to the others. Therefore, it will be necessary to better investigate this possible difference in future studies.