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At the roots of Spatial Numerical Association: from behavioural observation to Neural Basis

Periodic Reporting for period 1 - SNANeB (At the roots of Spatial Numerical Association: from behavioural observation to Neural Basis)

Reporting period: 2018-10-01 to 2020-09-30

Number knowledge and processing is fundamental for everyday living. In humans, numerical abilities are present pre-linguistically in infancy. Qualitatively and quantitatively similar mathematical performance has been observed in different species, including human adults, consistent with a shared, ancestral, nonverbal numerical mechanism. Uniquely human mathematical abilities appear to be scaffolded on this ontogenetically and evolutionarily ancient “number sense”. A peculiar characteristic of numbers concerns their strong association with space: humans represent numbers on a mental number line oriented from left to right. Traditionally, the spatial numerical association, SNA, has been considered a by-product of culture. Recently, evidence on the SNA in animals suggests that it originates from pre-linguistic and biologically determined precursors.
In the SNANeB project I’m studying the origin of SNA in day-old domestic chicks and monkeys, thus addressing the origin of the SNA in the absence of language or culture. Better understanding of the brain mechanisms behind the SNA would be critical for disentangling the wellspring of number-space mapping and for understanding how this could affect mathematical reasoning, providing a valuable early intervention for infants with potential problems in mathematical comprehension.
The aim of the first study was to understand whether numerical magnitude prompts attention toward the left or the right space in monkeys. Young and naive monkeys learned to respond to a target, which appeared in different positions on a monitor. When the stimuli did not convey numerical information, monkeys equally responded on either side. Whenever presented with increasing numbers, monkeys showed either a left or a right bias. Though present in monkeys, SNA is either left-to-right or right-to-left oriented, depending on the individual.
A second objective was to determine whether action selection is modulated by numerical magnitude. New young and inexperienced monkeys learned to select a target which could appear within a single dot on a monitor. In probe trials, we varied the number of dots on the monitor, which could vary in number from 2 to 10, and target’s ordinal position; 1st, 2nd, 3rd or 4th. When the series comprised a small number of dots (two), monkeys performed better when the target was on the left, when the series comprised a larger number (six or ten) they identified more correctly targets on the right side. A series of control experiments showed that monkeys use both spatial and numerical cues, supporting the hypothesis that spatial and numerical information are strongly associated.
The outgoing phase of the SNANEB project enlarged our knowledge on spatial numerical association, SNA, in non-human primates. We demonstrated that monkey showed consistent tendencies for spatial representations of numerousness and that numerical magnitudes modulate responses on ordinal target. Monkeys better identified left targets when responding to small numerical magnitudes and right target when responding to larger ones. The first two studies were based on an innovative method, which integrates SNA and ordinal identification, providing evidence on how such a spatially oriented representation of numbers may support counting acquisition.
The returning ongoing phase of the SNANEB project meets the challenge to unveil the neural substrates of SNA. Up to now the SNA has been described in different species, but the neural correlates of this association are still unknown. I will explore the effects of prenatal experience on SNA in the domestic chick. In this animal model, prenatal factors, as simple as exposure to light, influence later cognitive abilities. Nevertheless it remains unexplored if light stimulation has any effect on numerical abilities and on SNA. Since light stimulation positively affect cognitive performance, I expect chicks hatched from light incubated eggs to perform better on numerical tasks and to show a stronger SNA. Moreover, I will investigate the role of the two cerebral hemispheres in SNA. In the avian brain, the contralateral hemisphere mainly elaborates the visual input to each eye. Thus I’ll study the contribution of each hemisphere by comparing the performance of chicks tested in three different conditions of vision: binocular, left monocular and right monocular. I would expect an advantage of the right hemisphere in dealing with spatial information; as a consequence I would expect a stronger SNA whenever the behavioral response is guided by the right hemisphere.
Overall this project will help in determining the origin of SNA and the underlying neural representation. This may permit optimized design of clinical applications to enhance numerical comprehension. Last but not least, the obtained outcomes as well as the experimental design might provide a valuable early interventions for infants with potential problems in mathematical comprehension, as occurs in Williams syndrome or dyscalculia.