Human laterality for manipulation and gestural communication related to 60 everyday activities: Impact of multiple individual-related factors.

Literature on laterality emphasises the importance of implementing a comprehensive investigation of humans' and non-humans' laterality for both non-communication and communication functions. Adopting a global approach should enhance our understanding of the mechanistic drivers of human brain functional lateralisation and help to explore further the nature of the left-hemispheric systems for both functions. This study investigated human laterality for both functions by taking, for the first time, numerous behaviours and multiple potential influential factors into consideration. We analysed replies to the Rennes Laterality Questionnaire that takes into account simultaneously: participants' behavioural, demographic and social characteristics as well as their genetic/social learning components and collateral factors such as health problems. We collected and analysed a large data set including 450,220 item responses (317,594 items related to behavioural laterality and 132,626 items related to personal information) by 5904 participants. The majority of participants were right-lateralised for nine behavioural categories. The laterality of right-lateralised individuals for the behaviours considered varied very little between behavioural categories, contrary to the laterality of ambiguously- and left-lateralised individuals. This is the first evidence of the stability of right-lateralised individuals and the relative flexibility of ambiguously- and left-lateralised individuals with regards to behavioural laterality related to 60 everyday activities. Moreover, the laterality patterns of our study population were linked in particular to the following individual-related factors: demographic characteristics (current continent of residence), social characteristics (socio-professional group and study level), and collateral factors (writing hand, forced right-hand use, guiding eye, and health problems related to ear and back). We discuss our findings in relation to the evolutionary roots of human brain lateralisation for non-communication and communication functions.