Doctoral Dissertation Improvement Grant: Lateralization of Tool Making and Language in the Brain

Indiana University, Bloomington IN

Investigators

Abstract

This doctoral dissertation project examines the relationship between handedness and functional brain organization, specifically for language and toolmaking. Results from recent brain imaging studies on stone tool manufacture show that similar brain networks are active for toolmaking and language, leading to hypotheses about the co-evolution of language and technology in the human lineage. One unexplored behavior that may be relevant to these hypotheses is the human trait of handedness. Over 85% of living humans are right-handed, and handedness has been shown to relate to brain organization specifically for language, toolmaking, and other important behaviors. Some have argued that tracking the evolution of population-wide right-hand preference may help to understand population-level changes in other important traits, as handedness evolution can be used as a proxy for the evolution of hemispheric specialization in the brain. However, researchers need to be sure that handedness associates well with functional brain activity in modern humans, specifically for language and toolmaking, to make sure this proxy relationship is applicable to the archaeological record. The doctoral student will collect neuroimaging data from human participants (50% left-handed) who will complete stone toolmaking, language, and visuospatial tasks while undergoing functional Magnetic Resonance Imaging (fMRI) scanning. Before being scanned, participants will complete several assessments of handedness and also learn to make simple stone tools. This will be the first study of left-handers within the context of stone tool making neuroimaging, and it will also be the first comparison of brain networks underlying stone toolmaking to both language and visuospatial attention in the same participants. The specific questions to be answered are: (1) Which methods are best for characterizing participant handedness (behavioral measures, surveys, or a mix of both)? (2) Are there common brain areas active for stone toolmaking, language, and spatial skills (and in which hemisphere)? (3) Does hemispheric specialization for these tasks associate with participant handedness? This study has clear implications for those who study the evolution of handedness in hominins, but it is also significant for wider discussions on the evolution of human cognition and language. Directly showing that handedness corresponds to functional brain activity for these behaviors will provide further motivation to examine their evolutionary contexts and histories. If reliable methods can be established for determining handedness in skeletal remains and stone tool assemblages researchers can make more informed interpretations about human ancestors and their behaviors. If handedness does not correspond to brain networks for toolmaking and language, researchers interested in the evolution of technology, language, and cognition can focus on other topics for future research. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.