Hemispheric Specialization Tied to Lateralized Motor Preference in Human and Non-Human Primates

In literature there are large discrepancies about methods to assess cerebral lateralization in both human and nonhuman primate populations. This study aimed to allow valid comparisons across different primate species by employing a quantitative Multidimensional Method. A comprehensive range of interactions with both social and non-social targets were considered to verify which aspects might elicit the manifestation of lateralized behaviours underpinned by asymmetrical neuronal functions. Spontaneous activities were observed in two groups of zoo great apes, chimpanzees (Pan troglodytes) and gorillas (Gorilla gorilla gorilla), and a group of 3-4 year-old typical pre-school children. Results demonstrated a strong consistency in both human and non-human species for a right-hand/left hemisphere dominance during contact with inanimate targets (i.e. objects and environmental items), suggesting a evolutionary hemispheric specialization influenced by object animacy. Additionally, both great ape species significantly preferred to keep conspecifics closer than 3 metres to their left during manual activities, suggesting a right hemisphere specialization for emotion processing. Only the silverback gorilla (alpha male) manifested the opposite pattern, potentially related to his hierarchical role within the gorilla society. No side preference was found in typical children however, their young age may indicate that they are still undergoing hemispheric development for emotion processing. This study supports an evolutionary origin of hemispheric specialization underling manipulative and social asymmetric behaviours that occurred prior to the split of humans from great apes

How Ecology Could Affect Cerebral Lateralization for Explorative Behaviour in Lizards

As recent studies have shown a left-eye preference during exploration in Podarcis muralis, which could be strictly related to its territoriality, we tested the same behaviour in a similar species, but one living in different habitats and showing a different ecology. In particular, we assessed the preferential turning direction in adults of a non-territorial lizard, Zootoca vivipara, during the exploration of an unknown maze. At the population level, no significant preference emerged, possibly for the lack of the territorial habit and the characteristics of the natural environment. Nevertheless, females turned to the left more frequently than males did. We hypothesize this as a motor bias, possibly due to a necessity for females to be coordinated and fast in moving in the environment, because of their viviparous condition and the resultant reduction of physical performance during pregnant periods, which are likely to increase vulnerability to predators

Target animacy influences gorilla handedness

Abstract We investigated the unimanual actions of a biological family group of twelve western lowland gorillas (Gorilla gorilla gorilla) using a methodological approach designed to assess behavior within social context from a bottom-up perspective. Measures of both the lateralization of unimanual actions (left, right) and the target of the action (animate, inanimate) were assessed during dual, synchronized video observations of naturalistic behavior. This paper demonstrates a corelationship between handedness and the animate quality of the target object. Analyses demonstrated a significant interaction between lateralized unimanual actions and target animacy and a right-hand bias for actions directed toward inanimate targets. We suggest that lateralized motor preference reflects the different processing capabilities of the left and right hemispheres, as influenced by the emotive (animate) and/or functional (inanimate) characteristics of the target, respectively

Human handedness: an inherited evolutionary trait

Our objective was to demonstrate that human population-level, right-handedness, is not species specific, precipitated from language areas in the brain, but rather is context specific and inherited from a behavior common to both humans and great apes. In general, previous methods of assessing human handedness have neglected to consider the context of action, or employ methods suitable for direct comparison across species. We employed a bottom-up, context-sensitive method to quantitatively assess manual actions in right-handed, typically developing children during naturalistic behavior. By classifying the target to which participants directed a manual action, as animate (social partner, self) or inanimate (non-living functional objects), we found that children demonstrated a significant right-hand bias for manual actions directed towards inanimate targets, but not for manual actions directed towards animate targets. This pattern was revealed at both the group and individual levels. We used a focal video sampling, corpus data-mining approach to allow for direct comparisons with captive gorillas (Forrester et al. in Anim Cogn 14(6):903–907, 2011) and chimpanzees (Forrester et al. in Anim Cogn in press, 2012). Comparisons of handedness patters support the view that population-level, human handedness, and its origin in cerebral lateralization is not a new or human-unique characteristic. These data are consistent with the theory that human right-handedness is a trait developed through tool use that was inherited from an ancestor common to both humans and great apes