Research reportThere is more to the picture than meets the rat: A study on rodent geometric shape and proportion preferences

- We examined exploration in tripartite metal objects with 1.2; 1.618 and 1.8 ratios in adult rats.
- Rats preferred 1.2 object ratio composition, independently of the maze object location.
- Rats did not disclose any preference for novelty when metal spheres were presented before cylinders.
- Rats preferred metal spheres more than cylinders when both were presented at the same time.
- The main rat external body ratios were more related to 1.2 ratio than to 1.6 or 1.8 ratios.

In rodents, the novel object preference test has been used as a behavioral parameter for evaluation of neotic exploratory behavior, and also for memory consolidation tasks. Geometric patterns of this preference are poorly understood, and may vary among species. We evaluated in Wistar rats (Rattus norvergicus) a possible exploration preference considering aluminum tripartite rounded and cylindrical objects of different proportions: 1.2; 1.618; 1.8. At the first day, animals were exposed to 1.2; 1.6 and 1.8 rounded objects. At 24 h after, these animals were exposed to the same objects, together with three new steel cylindrical objects (same proportions). ANOVA and T tests were used to quantify object exploration for each animal (p < 0.05). Data analysis pointed to a longer exploration time of the object 1.2 at the three different protocols indicating a preference pattern on the first day exposition. On the second day the exploration was similar in both familiar and unfamiliar objects, revealing no novel object preference for cylinders. However, we found an object preference related to the 1.2 proportion (balls plus cylinders), in two of three position protocols. In addition, on a single exposition with both cylinders and rounded objects, rats revealed a rounded object preference. The 1.2 preference disclosed by rats also reflected the proportion of their body. From nine main measures of body ratios, seven were close to 1.2 ratio. The correspondence between body ratios and object preference may be explained by habituation learning and by sexual selection, and highlight innate factors regarding aesthetic preferences among species.