Lateralized motor control in spider monkeys ( Ateles geoffroyi ): Evidence from visual-spatial working memory tasks

The primate order has received considerable interest in studies on lateralized behaviour due to their hemisphere specialization and potentially major implications for the evolution of the human cerebral cortex. The development of the prefrontal and association regions is required for complex behaviours, and there is evidence that some species show hemispheric specialization in the performance of executive functions. However, laterality in relation to working memory in New World monkeys has received little attention. The main aim of this study was to explore the use of the hands and the tail in spider monkeys (Ateles geoffroyi) while performing two visual-spatial delayed match-to-sample (DMTS) tasks. Eight juvenile male spider monkeys raised in outdoor rain forest enclosures were studied. They were tested on two tasks over a period of 20 days. The first DMTS task had a 15-sec delay and used two different containers to hide a reward. The second had a 60-sec delay and used four different containers. Spider monkeys showed a robust and consistent left-hand preference during both acquisition and execution of DMTS tasks, occasionally accompanied by left-side tail use. The left-hand preference provide evidence for lateralized motor control and contribute to understanding hemispheric specialization to working memory in nonhuman primates.