Background
- Many vertebrate species exhibit brain hemisphere lateralization as evidenced by a preference for one side of the body or the other during postural and feeding behavior.
- Because nerves from one side of the body link to the opposite side of the brain, the right hemisphere largely orchestrates functionality of the body’s left side and vice versa.
- MacNeilage et al. (2009) hypothesize that early in vertebrate evolution. They argue that the left hemisphere, which directs the right side of the body, has become primarily responsible for exploratory behavior such as vigilance. The right hemisphere, which directs the left side of the body, has become responsible for innate behavior, such as fear or escape responses. The lateralization of hemispheres may therefore link personality and handedness because right-handed individuals may tend to exhibit stronger personality traits of boldness and exploration, while left-handed individuals may be more cautious.
- In contrast, others suggest that the right hemisphere tends to produce negative emotions and thus aversion to novel stimuli (Bracinni & Caine 2009). Therefore, they suggest that right-handed individuals will be more bold and exploratory.
- We tested response time to novel foods as a function of handedness in zoo-living golden lion tamarins. By the MacNeilage et al. (2009) hypothesis, we would predict that left-handed individuals would be quicker to approach, sniff, and taste novel foods. Conversely, according to Braccini & Caine (2009) we would predict that right-handed individuals would be quicker.
Methods
Results
Figure 1. The handedness of individuals categorized by z-scores. All the individuals were handed, 71% were right handed.
Fig 2. Figure 5. Individuals did not differ in their latencies to approach (General Linear Mixed Model – Right: 34.27 ± 1.80s; Left: 36.21 ± 1.91s, Likelihood Ratio Test (LRT) p = 0.745) or sniff (Right: 52.80 ± 1.64s; Left: 52.42 ± 1.72s, LRT p = 0.315). Individuals did vary significantly by latency to Taste (Right: 127.17 ± 1.62s; Left: 90.60 ± 1.70s, LRT p = 0.038) the novel foods we presented to them.
Discussion
- Golden lion tamarins foraging is highly specialized in that they use their hands to explore substrates. In contrast, common marmosets typically contact foraging substrates with their mouths (Singer and Schwibbe, 1998). This predisposition to use their hands is an adaptive strategy for finding hidden prey, such as tree frogs and solitary insects.
- All of the golden lion tamarins in our study used one hand significantly more often than the other. The handedness seen in our study suggests that the brain hemispheres of golden lion tamarins are lateralized.
- We found that left-handed golden lion tamarins were significantly quicker to taste novel foods and they tasted these foods more frequently than right-handed individuals. These results support MacNeilage et al.’s (2009) hypothesis that left-handed individuals will be more exploratory than right-handed individuals. In contrast, previous studies have found that right-handed common marmosets exhibit more exploratory behavior towards novel objects compared to their left-handed conspecifics (Cameron & Rogers 1999, Piddington & Rogers 2013).
- The varied prior experiences of our study subjects may have influenced our results. The environments and past experiences of our subjects were not uniform because the study encompassed three different zoos and our subjects were housed in many different exhibits and in groups of different sizes and composition. These differences may well have influenced responses to novelty and overshadowed some links between personality and handedness. Furthermore, all of our subjects had spent their lives in captivity, which could have dulled their innate cautiousness to novelty due to the safety and consistency of the captive environment (Beck et al. 2003).
References
1. Beck, Maple, Stoinski, Bloomsmith. A behavioral comparison of captive-born, reintroduced golden lion tamarins and their wild-born offspring. Behaviour 2003;140(2):137-60.
2. Braccini, S. N., & Caine, N. G. (2009). Hand preference predicts reactions to novel foods and predators in marmosets (callithrix geoffroyi). Journal of Comparative Psychology, 123(1), 18.
3. Cameron, R., & Rogers, L. (1999). Hand preference of the common marmoset (callithrix jac-
chus): Problem solving and responses in a novel setting. Journal of Comparative Psychology, 113(2), 149.
4. MacNeilage PF, Vallortigara G, Rogers LJ. Origins of the left & right brain. Scientific American 2009;301(1):60-7.
5. Piddington, T., & Rogers, L. J. (2013). Strength of hand preference and dual task performance by common marmosets. Animal Cognition, 16(1), 127-135. doi:10.1007/s10071-012-0562-2 [doi]
6. Schwibbe M, Singer S. Right or left, hand or mouth: Genera-specific preferences in marmosets and tamarins. Behaviour 1999;136(1):119-45.