Abstract
Evidence has shown that a variety of vertebrates, including fish, can discriminate collections of visual items on the basis of their numerousness using an evolutionarily conserved system for approximating numerical magnitude (the so-called Approximate Number System, ANS). Here we combine a habituation/dishabituation behavioural task with molecular biology assays to start investigating the neural bases of the ANS in zebrafish. Separate groups of zebrafish underwent a habituation phase with a set of 3 or 9 small red dots, associated with a food reward. The dots changed in size, position and density from trial to trial but maintained their numerousness, and the overall areas of the stimuli was kept constant. During the subsequent dishabituation test, zebrafish faced a change (i) in number (from 3 to 9 or vice versa with the same overall surface), or (ii) in shape (with the same overall surface and number), or (iii) in size (with the same shape and number). A control group of zebrafish was shown the same stimuli as during the habituation. RT-qPCR revealed that the telencephalon and thalamus were characterized by the most consistent modulation of the expression of the immediate early genes c-fos and egr-1 upon change in numerousness; in contrast, the retina and optic tectum responded mainly to changes in stimulus size.
Highlights
Numerical abilities can be apparent in association with a symbolic and a non-symbolic system[1,2,3]
We aimed to identify the brain regions that are involved in quantity discrimination processes, using the expression of the immediate early genes (IEGs) c-fos and egr-1, which are widely employed as transient markers of neuronal activity[49] using a response to novelty, habituation/dishabituation paradigm
Data concerning the proportion of time spent near the stimulus were analyzed with a Kruskal-Wallis test with habituation (3 or 9 elements) and test (no change, change in number, change in shape, change in surface area, change in surface area)
Summary
Numerical abilities can be apparent in association with a symbolic and a non-symbolic system[1,2,3]. The former is a human-specific trait, which supports precise numerical determination through the use of symbols (e.g. Arabic or Roman numerals) belonging to a cultural tradition The latter is a language-independent, non-symbolic mechanism that exploits magnitude and approximation for representing numerical sets of physical elements in an analogue fashion, the so-called Approximate Number system (ANS). The ability to evaluate numerical information and compare quantities is thought to represent an ecological advantage in the interactions between organisms and their surrounding environment Animals exploit this ability in order to optimize foraging decisions[10], responses to aggressive behaviours[11,12], defence against predators or to predate efficiently[13,14], and to estimate the number of social companions[15,16,17]. There is evidence that, even in humans, subcortical regions can be crucially involved in response to numerousness[36]
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