Supplementary Material for: “Mind Over Muscle”: Neural and Biomechanical Signatures of Expertise in Early Stone Tool Use

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Introduction: Understanding the cognitive and biomechanical foundations of early hominin tool use represents a central focus in human evolutionary research. Although interdisciplinary work on early lithic technologies has explored each of these aspects separately, few experimental approaches have directly examined the interaction between neural and muscular systems during stone tool use. This study adopts a recently developed interdisciplinary approach to explore the impact of cumulative tool-related expertise (practical “know-how”) on the dynamic brain-body interplay required for efficient early hominin stone tool use. Methods: Our experimental design compares Experts (with extensive practical knapping experience), Intermediates (with only theoretical knowledge), and Novices (with neither) performing two of the earliest known stone tool behaviors in the fossil record: hammerstone nut-cracking and Oldowan-style flake cutting. Using simultaneous electroencephalographic and electromyographic recordings, we analyzed neural activity in the left-frontal, premotor/motor, and left-parietal cortices alongside selective muscular activation in the hands and forearms. Results: Our findings show that, during flake cutting, Experts display distinct beta-band neural activity in the left frontal and premotor/motor regions, and to a lesser extent in the left parietal region, accompanied by overall reduced muscular activation. In the nut-cracking task, Experts show reduced muscular effort and slightly elevated premotor/motor involvement, though to a much lesser degree. Importantly, Experts also present significant neural differences between the two tasks, suggesting task-specific cognitive strategies related to motor planning and coordination. In contrast, Novice participants demonstrate greater reliance on higher muscular effort and left-lateralized parietal regions, likely reflecting increased engagement of visuospatial processing and understanding tool function and mechanical knowledge. Conclusion: Altogether, these findings provide critical insights into the brain-hand interplay required for humanlike early stone tool use and highlight cumulative practical knowledge (“know-how”) as a decisive factor of neuromechanical efficiency in early hominin technological behavior. They also encourage future experimental research on increased sample sizes to adopt integrated methods that jointly consider neural and muscular dynamics.

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