Mapping numerosities into space by zebrafish

Evidence suggests that in humans, numbers are arranged along a mental number line oriented from left to right. Recently, apparently similar phenomena have been described for non-symbolic numerosities in pre-verbal infants and non-human animals. We trained zebrafish (Danio rerio) to associate a stimulus with a certain number of elements (e.g. 5 elements) with a reward. In a test with a different number of elements, zebrafish spontaneously associate a smaller numerosity (e.g. 2 elements) with the left space and a larger numerosity (e.g. 8 elements) with the right space. Furthermore, zebrafish associated the same numerosity (5 elements) with the left or the right space depending on the size of the numerosity they were familiarized with during training (either 2 or 8 elements). These findings open the doors to the possible genetic investigation of the mapping of number to space.