Reaching for a domain-general syntax: processing linguistic structures and grasping an object with a tool share similar neural codes in the basal ganglia

Are actions organized like sentences? Recent evidence showed reciprocal transfer between tool use and syntactic comprehension, reflecting shared basal ganglia (BG) resources for action and language. The proposed mechanism is that embedding a tool into the motor plan increases the hierarchical structure of actions paralleling the organization of sentences. If so, overlap with linguistic computations should emerge specifically during the initiation and/or reach-to-grasp phase, when tool embedding dynamically updates the relation with the target, rather than when the object is stably held in the tool grip. Forty French native speakers underwent fMRI while performing a sentence comprehension (object vs. subject relatives), and a motor task (with pliers vs. hand). Only the reach-to-grasp phase with the tool elicited neural patterns resembling those of object-relatives, within overlapping BG regions. This phase-specific convergence identifies the BG as a hub for domain-general hierarchical computations, unifying syntactic embedding for language and tool use.