Shared Brain Lateralization Patterns in Language and Acheulean Stone Tool Production: A Functional Transcranial Doppler Ultrasound Study

Abstract

BackgroundThe popular theory that complex tool-making and language co-evolved in the human lineage rests on the hypothesis that both skills share underlying brain processes and systems. However, language and stone tool-making have so far only been studied separately using a range of neuroimaging techniques and diverse paradigms.Methodology/Principal FindingsWe present the first-ever study of brain activation that directly compares active Acheulean tool-making and language. Using functional transcranial Doppler ultrasonography (fTCD), we measured brain blood flow lateralization patterns (hemodynamics) in subjects who performed two tasks designed to isolate the planning component of Acheulean stone tool-making and cued word generation as a language task. We show highly correlated hemodynamics in the initial 10 seconds of task execution.Conclusions/SignificanceStone tool-making and cued word generation cause common cerebral blood flow lateralization signatures in our participants. This is consistent with a shared neural substrate for prehistoric stone tool-making and language, and is compatible with language evolution theories that posit a co-evolution of language and manual praxis. In turn, our results support the hypothesis that aspects of language might have emerged as early as 1.75 million years ago, with the start of Acheulean technology.

Flake morphology as a record of manual pressure during stone tool production

“…Given the high cognitive demands associated with stone tool production techniques, a great deal of this attention has been focused on how the lithic archaeological record may inform our understanding of the evolution of human cognitive capabilities (Beaune et al, 2009;Gamble et al, 2014). These capabilities include the evolution of language, imitation, complex technological capabilities, increased brain size, complex social systems, cognitive and manual lateralisation, spatial cognition and shape recognition (Ambrose, 2010;de Beaune, 2004;Gowlett et al, 2012;Morgan et al, 2015;Schillinger et al, 2015;Stout, 2011;Stout et al, 2008;Uomini and Meyer, 2013;Wynn, 2002). Comparatively little work has investigated how lithic artefacts may be used to further our understanding of the evolution of human musculoskeletal anatomy and biomechanical capabilities.…”

Test, Model, and Method Validation: The Role of Experimental Stone Artifact Replication in Hypothesis-driven Archaeology

“…Results of such tests are not necessarily meant to be directly compared to archaeological data but instead to serve as a means of formally assessing and understanding the bounds of what is practically achievable when making or using stone tools in order to support or falsify potential motivating factors underlying patterns of tool production, use, morphology, and variability (Diez-Martin and Eren 2012; Lycett and Eren 2013b). There are several broad avenues of inquiry that have been investigated by means of experimental tests, including comparative morphology (Driscoll 2011;Eren and Lycett 2012;Gurtov, Buchanan, and Eren 2015;Presnyakova et al 2015;Williams and Andrefsky 2011); process controls (Patten 2002(Patten , 2005(Patten , 2009); tool use-life (Shott 2002); cognition and language (Geribas, Mosquera, and Vergès 2010;Mahaney 2014;Morgan et al 2015b;Putt, Woods, and Franciscus 2014;Stout et al 2000;Uomini and Meyer 2013); biomechanics (Faisal et al 2010;Key and Lycett 2011;Key and Dunmore 2015;Nonaka, Bril, and Rein 2010;Rolian, Lieberman, and Zermeno 2011;Richmond 2012, 2014); and the influence of stone raw material differences on lithic form (Archer and Braun 2010;Eren et al 2014b), production technology (Bar-Yosef et al 2012), tool function Galán and Domínguez-Rodrigo 2014;Rodríguez-Rellán, Valcarce, and Esnaola 2013;Waguespack et al 2009;Wilkins, Schoville, and Brown 2014), knapper skill (Duke and Pargeter 2015;Sampson 2011b, Eren et al 2011c;Stout and Semaw 2006;Winton 2005), use-wear accru...…”

The role of experimental knapping in empirically testing key themes in the evolution of lithic technology: reduction intensity, efficiency and behavioural complexity

“…Recent neuropsychological research has found hierarchical organisation to be a common component in both stone tool production and syntactic language (Greenfield 1991;Higuchi et al 2009;Mahaney 2014;Morgan et al 2015;Stout and Chaminade 2012;Stout et al 2008;Uomini and Meyer 2013), with some arguing for a coevolution of complex language and tool making (Ambrose 2010;Morgan et al 2015). The evidence outlined in this study for the gradual evolution of hierarchical complexity in stone tool manufacture may therefore also reflect the evolution of the hierarchical elements of syntactic language.…”

“…Another approach has been to examine relative cognitive traits via scans of brain activity and blood flow (Stout and Chaminade 2007;Stout et al 2000;Stout et al 2008;Uomini and Meyer 2013).…”

“…It was therefore concluded that Neanderthals and their contemporaneous Homo sapiens employed toolkits requiring equivalent levels of behavioural complexity in their manufacture. With hierarchical complexity involved in both tool-making and syntactic language (Greenfield 1991;Higuchi et al 2009;Mahaney 2014;Morgan et al 2015;Stout and Chaminade 2012;Stout et al 2008;Uomini and Meyer 2013), the evidence for expanding levels of behavioural complexity required for tool manufacture may also reflect a growing capacity for complex language. With evidence of language preserving poorly in the archaeological record, the archaeological utility of this paper may go beyond mere technological interpretations.…”