Natalie Uomini, Larry Barham, Michal Paradysz and Georg Meyer
The possible co-evolution of brain areas supporting language and tool-use has been the focus of intense debate in recent years. Functional neuroimaging data can help us identify signals of coevolution (exaptation) or the absence of functional overlap indicating separate evolution. There is, however, a scarcity of neuroimaging data on both language and stone tool-use from the same participants. We used fMRI to compare directly brain activations in the same individuals, with matched paradigms for action observation of stone-age tool-use, modern tool-use, and speech syllables. In two action observation experiments, we found signiFicant increases in functional activation in bilateral frontal mirror neuron regions (IFG and PMC), as well as the classic lateralised areas in left SMG and IPL. Univariate analyses revealed overlapping activation clusters in the mirror neuron network. A multivariate analysis, MVPA, showed overlapping but separable activation patterns for speech and tool-use. Our study failed to replicate the lateralised activations for stone tool-use reported in previous studies. Taken together, our Findings support the hypothesis of co-evolution (exaptation) for tool-use and language. Fossil evidence from human brain evolution suggests that bilateral frontal areas are a key region which experienced the First selection pressures, with increasing asymmetry of temporal lobes over time. We propose that increased processing demands on mirror neuron regions for both stone toolmaking and language skills could explain why these regions showed the earliest trace of brain reorganization in our fossil ancestors starting 3 million years ago.