Several theories have considered language to have evolved from tool use. In a recent article in the journal Science, Thibault and his colleagues tested their theory that tool use requires ‘…integrating an external object as a body part and embedding its functional structure in the motor program’. In their view, this adds a ‘hierarchical level into the motor plan’ that involves ‘modifying relationships among interdependent subcomponents’. Thibault and colleagues noted that ‘embedded structures also exist in language’ and that syntax is the function used to organize linguistic hierarchies. Thus, they argue that syntax is a function common to both language and tool use and conducted two experiments to test this hypothesis.

In the first experiment, subjects performed both a syntax task and a novel tool use task while brain images were acquired using functional magnetic resonance imaging (fMRI). This imaging modality captures blood oxygenation changes in the brain and serves as a proxy measure for neuronal activation. In the tool use task, subjects had to use a long tong-like tool to precisely move small items on a board. In the syntax task, subjects had to read sentences with complex syntax (e.g., The writer that the poet admires writes the paper) and then select a true statement about the sentence from among four possibilities (e.g., The writer writes the paper). These tasks were first compared simple syntax and simple movement tasks, and then to each other. The main finding was that a small region of the basal ganglia was commonly activated by both tool use and language syntax.

It is notable that the overlapping activation occurred in the basal ganglia and not in the left inferior frontal gyrus (IFG). The left IFG is the location of Broca’s area which when damaged in humans causes an expressive aphasia and difficulty in processing syntax. The left IFG is also considered by some investigators to be the location in humans that is analogous the mirror neuron area in non-human primates. Mirror neurons are those that respond both to motor actions performed by the agent, but also in response to observing those actions performed by another agent. Thibault and colleagues observed activation in the left IFG for both the syntax and the tool use task, but the activations were spatially distinct and did not overlap.

In the second experiment, Thibault and colleagues determined whether the shared circuitry between the two tasks was amenable to cross training. Two groups of subjects were tested. One group was trained on the language syntax task and then tested with the novel tool use task. The other group was trained on the novel tool use task and tested on the syntax task. In both groups, training on one task improved performance on the other task. This supported their overall conclusion that a common neural circuitry was being used in both tasks.

Students interested in learning more about theories linking tool use and language can consult a 2012 special issue of the Philosophical Transactions of the Royal Society devoted to this interesting topic.

References:

Thibault, S., Py, R., Gervasi, A. M., Salemme, R., Koun, E., Lövden, M. et al. (2021). Tool use and language share syntactic processes and neural patterns in the basal ganglia. Science, 374(6569).

Steele, J., Ferrari, P. F., & Fogassi, L. (2012). From action to language: comparative perspectives on primate tool use, gesture and the evolution of human language. Philos Trans R Soc Lond B Biol Sci, 367(1585), 4-9.