Lithic industries, modern tools, and language: An evolutionary perspective through fMRI.

Abstract

Tool use is a defining cognitive ability of the human species, relying on technical reasoning-a causal and analogical understanding of physical principles. Neuroarchaeological studies suggest that lithic tool use engaged a specialized frontoparietal network, which evolved into the left-lateralized network observed for modern tools. This network includes the left inferior parietal lobule, particularly the area PF, linked to technical reasoning, and the left inferior frontal gyrus, which is both involved in tool use and language. Since these latter two domains are based on hierarchical structuring, organizing embedded constraints, the common involvement of the left inferior frontal gyrus has been proposed as evidence of a co-evolutionary trajectory. Using fMRI, we investigated whether increasing mechanical complexity modulates frontoparietal activity and whether lithic and modern tools engage a common neural network. Participants performed a tool evaluation task, in which they assessed the functionality of both tool types across three levels of complexity designed to reflect embedded constraints. Our results revealed stronger functional connectivity between the left area PF and the left pars opercularis of the inferior frontal gyrus as mechanical complexity increased. The results also confirmed common activation for both tool types. By demonstrating that frontoparietal connectivity scales with complexity in tool evaluation, our study provides new insights into the neurocognitive foundations of tool use. These findings contribute to the broader discussion of a co-evolutionary relationship involving technical reasoning, tool making, and language, highlighting the role of hierarchical processing as a potentially shared computational principle.