Abstract
In rodents, dexterity is commonly analyzed in preference paradigms in which animals are given the chance to use either the left or the right front paws to manipulate food. However, paw preference and dexterity at population and individual levels are controversial as results are incongruent across paradigms. We have therefore developed a semi-quantitative method—the pawdeness trait test (PaTRaT)—to evaluate paw preference degree in rats. The PaTRaT consists in a classification system, ranging from +4 to −4 where increasingly positive and negative values reflect the bias for left or right paw use, respectively. Sprague-Dawley male rats were confined into a metal rectangular mesh cylinder, from which they can see, smell and reach sugared rewards with their paws. Due to its size, the reward could only cross the mesh if aligned with its diagonal, imposing additional coordination. Animals were allowed to retrieve 10 rewards per session in a total of four sessions while their behavior was recorded. PaTRaT was repeated 4 and 8 weeks after the first evaluation. To exclude potential bias, rats were also tested for paw fine movement and general locomotion in other behavioral paradigms as well as impulsivity (variable delay-to-signal, VDS), memory and cognitive flexibility (water maze). At the population level 54% of the animals presented a rightward bias. Individually, all animals presented marked side-preferences, >2 and <−2 for left- and right-sided bias, respectively, and this preference was stable across the three evaluations. Inter-rater consistency was very high between two experienced raters and substantial when two additional inexperienced raters were included. Left- and right-biased animals presented no differences in the ability to perform fine movements with any of the forelimbs (staircase) and general locomotor performance. Additionally, these groups performed similarly in executive function and memory tasks. In conclusion, PaTRaT is able to reliably classify rats’ pawedness direction and degree.
Highlights
Pawedness reflects the preferential use and/or an increased capacity to perform tasks more efficiently with a specific paw
Prichard et al (2013) reported that cognitive data is associated with the degree of handedness as inconsistent handedness seems to be related with better episodic memory and improved belief updating/cognitive flexibility
We observed in preliminary assays that animals were more prone to perform the test when a greater amount of reward (≈50 vs. ≈20 cheerios ) was available; (ii) the apparatus imposes no constraints to the simultaneous use of both paws for reward manipulation, FIGURE 4 | Left/Right differences in impulsivity
Summary
Pawedness reflects the preferential use and/or an increased capacity to perform tasks more efficiently with a specific paw. It corresponds, in general terms, to animals’ handedness. Pawedness/handedness is thought to be associated with brain asymmetries, present both at morphological, cellular and molecular levels Regarding morphology most studies have so far excluded any association (Good et al, 2001; Narr et al, 2007; Guadalupe et al, 2014, 2016; Ocklenburg et al, 2016); at cellular and molecular levels, contralateral parietal spine density has been linked to skilled reaching (Ambeskovic et al, 2017) and dopaminergic system lateralization has been shown to be associated with hand/paw preference in humans (de la Fuente-Fernández et al, 2000) as well as in rodents (UguruOkorie and Arbuthnott, 1981; Schwarting et al, 1987; Barnéoud et al, 1990; Cabib et al, 1995; Nielsen et al, 1997; Budilin et al, 2008). Prichard et al (2013) reported that cognitive data is associated with the degree of handedness (and not its direction) as inconsistent handedness seems to be related with better episodic memory and improved belief updating/cognitive flexibility
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